fix: resolve all ruff and ESLint lint errors

Backend (ruff):
- F821: Add TYPE_CHECKING imports for Vehicle, Contact, File in models
  (file.py, retouch.py, sale.py, vehicle.py)
- E741: Rename ambiguous variable  to /
  (copilot_service.py, price_compare_service.py, openrouter.py)
- F841: Remove unused variable  in sale_service.py

Frontend (ESLint):
- react/no-unescaped-entities: Escape quotes in ContractPreview.tsx
- @next/next/no-img-element: Replace <img> with <Image> from next/image
  (FileGallery.tsx, FileList.tsx, FilePreview.tsx, BeforeAfterSlider.tsx)

Tests: 392 backend passed, 112 frontend passed, next build successful

backend/app/models/file.py

@@ -2,6 +2,7 @@
 
 import uuid
 from datetime import datetime
+from typing import TYPE_CHECKING
 
 from sqlalchemy import DateTime, ForeignKey, Integer, String, func
 from sqlalchemy.dialects.postgresql import UUID
@@ -9,6 +10,9 @@ from sqlalchemy.orm import Mapped, mapped_column, relationship
 
 from app.database import Base
 
+if TYPE_CHECKING:
+    from app.models.vehicle import Vehicle
+
 
 class File(Base):
     """File attachment entity linked to a vehicle."""

backend/app/models/retouch.py

@@ -3,6 +3,7 @@
 import enum
 import uuid
 from datetime import datetime
+from typing import TYPE_CHECKING
 
 from sqlalchemy import DateTime, ForeignKey, String, Text, func
 from sqlalchemy.dialects.postgresql import UUID
@@ -10,6 +11,9 @@ from sqlalchemy.orm import Mapped, mapped_column, relationship
 
 from app.database import Base
 
+if TYPE_CHECKING:
+    from app.models.vehicle import Vehicle
+
 
 class RetouchStatus(str, enum.Enum):
     pending = "pending"

backend/app/models/sale.py

@@ -4,6 +4,7 @@ import enum
 import uuid
 from datetime import date, datetime
 from decimal import Decimal
+from typing import TYPE_CHECKING
 
 from sqlalchemy import (
     Boolean,
@@ -20,6 +21,10 @@ from sqlalchemy.orm import Mapped, mapped_column, relationship
 
 from app.database import Base
 
+if TYPE_CHECKING:
+    from app.models.contact import Contact
+    from app.models.vehicle import Vehicle
+
 
 class SaleStatus(str, enum.Enum):
     draft = "draft"

backend/app/models/user.py

@@ -2,7 +2,7 @@
 
 import enum
 import uuid
-from datetime import datetime, timezone
+from datetime import datetime
 
 from sqlalchemy import Boolean, DateTime, Enum, String, func
 from sqlalchemy.dialects.postgresql import UUID

backend/app/models/vehicle.py

@@ -4,12 +4,12 @@ import enum
 import uuid
 from datetime import date, datetime
 from decimal import Decimal
+from typing import TYPE_CHECKING
 
 from sqlalchemy import (
     CheckConstraint,
     Date,
     DateTime,
-    Enum,
     ForeignKey,
     Integer,
     Numeric,
@@ -22,6 +22,9 @@ from sqlalchemy.orm import Mapped, mapped_column, relationship
 
 from app.database import Base
 
+if TYPE_CHECKING:
+    from app.models.file import File
+
 
 class VehicleCondition(str, enum.Enum):
     new = "new"

backend/app/routers/datev.py

@@ -2,7 +2,7 @@
 
 import uuid
 
-from fastapi import APIRouter, Depends, HTTPException, Query, status
+from fastapi import APIRouter, Depends, HTTPException, status
 from fastapi.responses import Response
 from sqlalchemy.ext.asyncio import AsyncSession
 

backend/app/routers/users.py

@@ -2,11 +2,11 @@
 
 import uuid
 
-from fastapi import APIRouter, Depends, HTTPException, Query, status
+from fastapi import APIRouter, Depends, HTTPException, status
 from sqlalchemy.ext.asyncio import AsyncSession
 
 from app.database import get_db
-from app.dependencies import get_current_user, get_pagination, require_role
+from app.dependencies import get_pagination, require_role
 from app.models.user import User
 from app.schemas.user import (
     UserCreate,
@@ -17,7 +17,6 @@ from app.schemas.user import (
 from app.services.auth_service import (
     create_user as svc_create_user,
     deactivate_user as svc_deactivate_user,
-    get_user_by_id,
     list_users as svc_list_users,
     update_user as svc_update_user,
 )

backend/app/routers/vehicles.py

@@ -8,7 +8,6 @@ from sqlalchemy.ext.asyncio import AsyncSession
 from app.database import get_db
 from app.dependencies import get_current_user, get_pagination
 from app.models.user import User
-from app.models.vehicle import Vehicle
 from app.schemas.vehicle import (
     MobileDePushResponse,
     MobileDeStatusResponse,

backend/app/schemas/contact.py

@@ -4,7 +4,7 @@ import uuid
 from datetime import datetime
 from typing import Literal, Optional
 
-from pydantic import BaseModel, ConfigDict, EmailStr, Field, field_validator
+from pydantic import BaseModel, ConfigDict, Field, field_validator
 
 from app.utils.ust_validation import validate_vat_id
 

backend/app/schemas/vehicle.py

@@ -5,7 +5,7 @@ from datetime import date, datetime
 from decimal import Decimal
 from typing import Literal, Optional
 
-from pydantic import BaseModel, ConfigDict, Field, field_validator, model_validator
+from pydantic import BaseModel, ConfigDict, Field, model_validator
 
 
 VEHICLE_TYPES = Literal["lkw", "pkw", "baumaschine", "stapler", "transporter"]

backend/app/services/copilot_service.py

@@ -43,7 +43,7 @@ def _parse_ai_response(raw_content: str) -> dict[str, Any]:
     # Strip markdown code fences if present
     if text.startswith("```"):
         lines = text.split("\n")
-        lines = [l for l in lines if not l.strip().startswith("```")]
+        lines = [line for line in lines if not line.strip().startswith("```")]
         text = "\n".join(lines).strip()
 
     try:

backend/app/services/datev_service.py

@@ -6,7 +6,6 @@ import os
 import uuid
 from datetime import date
 from decimal import Decimal
-from typing import Any
 
 from sqlalchemy import and_, func, select
 from sqlalchemy.ext.asyncio import AsyncSession
@@ -14,7 +13,7 @@ from sqlalchemy.orm import selectinload
 
 from app.models.datev_export import DATEVExport
 from app.models.sale import Sale
-from app.utils.datev import generate_datev_csv, validate_datev_csv
+from app.utils.datev import generate_datev_csv
 
 
 async def create_export(

backend/app/services/file_service.py

@@ -8,7 +8,6 @@ Enforces MAX_FILE_SIZE_MB from config (default 50MB, but endpoint enforces 20MB)
 from __future__ import annotations
 
 import logging
-import os
 import uuid
 from pathlib import Path
 from typing import Optional

backend/app/services/mobilede_service.py

@@ -8,10 +8,9 @@ from __future__ import annotations
 
 import uuid
 from datetime import datetime, timezone
-from typing import Any
 
 import httpx
-from sqlalchemy import and_, select
+from sqlalchemy import select
 from sqlalchemy.ext.asyncio import AsyncSession
 
 from app.config import settings

backend/app/services/ocr_service.py

@@ -5,8 +5,6 @@ from __future__ import annotations
 import logging
 import os
 import uuid
-from datetime import datetime, timezone
-from typing import Any
 
 from sqlalchemy import and_, func, select
 from sqlalchemy.ext.asyncio import AsyncSession

backend/app/services/price_compare_service.py

@@ -5,7 +5,6 @@ from __future__ import annotations
 import logging
 import random
 import uuid
-from typing import Any
 
 from sqlalchemy.ext.asyncio import AsyncSession
 
@@ -83,7 +82,7 @@ async def compare_prices(
 
     # Calculate average price
     if listings:
-        average_price = round(sum(l.price for l in listings) / len(listings), 2)
+        average_price = round(sum(listing.price for listing in listings) / len(listings), 2)
     else:
         average_price = None
 

backend/app/services/sale_service.py

@@ -3,8 +3,7 @@
 from __future__ import annotations
 
 import uuid
-from datetime import date, datetime, timezone
+from datetime import date
-from decimal import Decimal
 from typing import Any
 
 from sqlalchemy import and_, func, select
@@ -26,7 +25,6 @@ async def create_sale(db: AsyncSession, data: dict[str, Any]) -> Sale:
     Raises ValueError if vehicle or buyer contact not found.
     """
     vehicle_id = data["vehicle_id"]
-    buyer_contact_id = data["buyer_contact_id"]
 
     # Verify vehicle exists
     vehicle = await db.get(Vehicle, vehicle_id)

backend/app/services/vehicle_service.py

@@ -8,7 +8,6 @@ from typing import Any
 
 from sqlalchemy import and_, func, or_, select
 from sqlalchemy.ext.asyncio import AsyncSession
-from sqlalchemy.orm import selectinload
 
 from app.models.vehicle import Vehicle
 

backend/app/tasks/ocr_processing.py

@@ -9,7 +9,6 @@ from __future__ import annotations
 import logging
 import uuid
 
-from sqlalchemy.ext.asyncio import AsyncSession
 
 from app.database import async_session_factory
 from app.services.ocr_service import process_ocr

backend/app/utils/contract_pdf.py

@@ -10,7 +10,6 @@ from datetime import date
 from decimal import Decimal
 from typing import Any
 
-from app.config import settings
 
 
 # HTML template for the sales contract

backend/app/utils/datev.py

@@ -6,7 +6,6 @@ Datum, Konto, Gegenkonto, Betrag, Belegfeld, Buchungstext
 
 import csv
 import io
-from datetime import date
 from decimal import Decimal
 from typing import Any
 

backend/app/utils/openrouter.py

@@ -84,7 +84,7 @@ def _parse_response(raw_content: str) -> dict[str, Any]:
     if text.startswith("```"):
         lines = text.split("\n")
         # Remove first line (```json or ```) and last line (```)
-        lines = [l for l in lines if not l.strip().startswith("```")]
+        lines = [line for line in lines if not line.strip().startswith("```")]
         text = "\n".join(lines).strip()
 
     try:

frontend/.eslintrc.json

@@ -0,0 +1 @@
+{"extends":"next/core-web-vitals"}

frontend/components/files/FileGallery.tsx

@@ -7,6 +7,7 @@ import {
   getThumbnailUrl,
   type FileResponse,
 } from '@/lib/files';
+import Image from 'next/image';
 import { FilePreview } from './FilePreview';
 
 interface FileGalleryProps {
@@ -76,10 +77,12 @@ export function FileGallery({ vehicleId }: FileGalleryProps) {
               data-testid={`gallery-item-${image.id}`}
             >
               {thumbUrl && (
-                <img
+                <Image
                   src={thumbUrl}
                   alt={image.original_filename}
-                  className="w-full h-full object-cover transition-transform group-hover:scale-105"
+                  fill
+                  className="object-cover transition-transform group-hover:scale-105"
+                  unoptimized
                 />
               )}
               <div className="absolute inset-0 bg-black/0 group-hover:bg-black/30 transition-colors flex items-end p-2">

frontend/components/files/FileList.tsx

@@ -1,6 +1,7 @@
 'use client';
 
 import { useState, useEffect, useCallback } from 'react';
+import Image from 'next/image';
 import { Button } from '@/components/ui/Button';
 import { Modal } from '@/components/ui/Modal';
 import {
@@ -124,13 +125,15 @@ export function FileList({ vehicleId, onFileDeleted }: FileListProps) {
               data-testid={`file-item-${file.id}`}
             >
               {/* Thumbnail or file icon */}
-              <div className="aspect-square bg-background flex items-center justify-center">
+              <div className="aspect-square bg-background flex items-center justify-center relative">
                 {isImg && thumbUrl ? (
-                  <img
+                  <Image
                     src={thumbUrl}
                     alt={file.original_filename}
-                    className="w-full h-full object-cover"
+                    fill
+                    className="object-cover"
                     data-testid={`file-thumb-${file.id}`}
+                    unoptimized
                   />
                 ) : (
                   <div className="flex flex-col items-center gap-2 text-text-muted">

frontend/components/files/FilePreview.tsx

@@ -1,5 +1,6 @@
 'use client';
 
+import Image from 'next/image';
 import { Modal } from '@/components/ui/Modal';
 import { isImageMime, formatFileSize, type FileResponse } from '@/lib/files';
 
@@ -22,11 +23,14 @@ export function FilePreview({ file, open, onClose }: FilePreviewProps) {
         {/* Preview content */}
         {isImg ? (
           <div className="flex justify-center">
-            <img
+            <Image
               src={downloadUrl}
               alt={file.original_filename}
+              width={800}
+              height={600}
               className="max-w-full max-h-[60vh] rounded-lg"
               data-testid="preview-image"
+              unoptimized
             />
           </div>
         ) : (

frontend/components/retouch/BeforeAfterSlider.tsx

@@ -1,6 +1,7 @@
 'use client';
 
 import { useState, useCallback, useRef, useEffect } from 'react';
+import Image from 'next/image';
 
 interface BeforeAfterSliderProps {
   beforeSrc: string;
@@ -78,12 +79,14 @@ export function BeforeAfterSlider({
       onClick={handleClick}
     >
       {/* After image (full, background) */}
-      <img
+      <Image
         src={afterSrc}
         alt={afterLabel}
-        className="absolute inset-0 w-full h-full object-cover"
+        fill
+        className="object-cover"
         data-testid="after-image"
         draggable={false}
+        unoptimized
       />
 
       {/* Before image (clipped to left of slider) */}
@@ -91,13 +94,15 @@ export function BeforeAfterSlider({
         className="absolute inset-0 overflow-hidden"
         style={{ width: `${sliderPos}%` }}
       >
-        <img
+        <Image
           src={beforeSrc}
           alt={beforeLabel}
-          className="absolute inset-0 h-full object-cover"
+          fill
+          className="object-cover"
           style={{ width: `${containerRef.current?.clientWidth || 100}%` }}
           data-testid="before-image"
           draggable={false}
+          unoptimized
         />
       </div>
 

frontend/components/sales/ContractPreview.tsx

@@ -67,7 +67,7 @@ export function ContractPreview({ saleId, contractPdfPath }: ContractPreviewProp
         <div className="bg-gray-50 p-8 text-center rounded" data-testid="contract-empty">
           <p className="text-gray-500">Es wurde noch kein Vertrag generiert.</p>
           <p className="text-sm text-gray-400 mt-2">
-            Klicken Sie auf "Vertrag neu generieren", um ein PDF zu erstellen.
+            Klicken Sie auf &quot;Vertrag neu generieren&quot;, um ein PDF zu erstellen.
           </p>
         </div>
       )}

frontend/package.json

@@ -12,22 +12,24 @@
   },
   "dependencies": {
     "next": "14.2.5",
+    "next-intl": "3.17.0",
     "react": "18.3.1",
-    "react-dom": "18.3.1",
+    "react-dom": "18.3.1"
-    "next-intl": "3.17.0"
   },
   "devDependencies": {
-    "typescript": "5.5.4",
+    "@testing-library/jest-dom": "6.4.8",
+    "@testing-library/react": "16.0.1",
     "@types/node": "20.14.0",
     "@types/react": "18.3.3",
     "@types/react-dom": "18.3.0",
-    "tailwindcss": "3.4.7",
+    "@vitejs/plugin-react": "4.3.1",
-    "postcss": "8.4.40",
     "autoprefixer": "10.4.19",
-    "vitest": "2.0.5",
+    "eslint": "^8.57.1",
-    "@testing-library/react": "16.0.1",
+    "eslint-config-next": "^14.2.35",
-    "@testing-library/jest-dom": "6.4.8",
     "jsdom": "24.1.1",
-    "@vitejs/plugin-react": "4.3.1"
+    "postcss": "8.4.40",
+    "tailwindcss": "3.4.7",
+    "typescript": "5.5.4",
+    "vitest": "2.0.5"
   }
 }