feat(T01): auth + user management + RBAC + base frontend + i18n

- Backend: FastAPI, JWT auth (HS256), bcrypt, RBAC middleware
- User CRUD (admin-only), soft-delete, pagination
- Pydantic BaseSettings config, async SQLAlchemy 2.0
- 50 backend tests, 88% coverage
- Frontend: Next.js 14 App Router, Tailwind, design tokens
- Login page, auth context, API client with auto-refresh
- i18n: next-intl, DE/EN (31 keys each)
- 6 base UI components (Button, Input, Card, Table, Modal, Toast)
- 12 frontend tests, npm build success

backend/app/routers/auth.py

@@ -0,0 +1,68 @@
+"""Auth router: login, token refresh, current user profile."""
+
+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
+from app.models.user import User
+from app.schemas.user import (
+    LoginRequest,
+    RefreshRequest,
+    TokenResponse,
+    UserResponse,
+)
+from app.services.auth_service import (
+    authenticate_user,
+    generate_token_pair,
+    refresh_access_token,
+)
+
+router = APIRouter(prefix="/auth", tags=["auth"])
+
+
+@router.post("/login", response_model=TokenResponse, status_code=status.HTTP_200_OK)
+async def login(
+    body: LoginRequest,
+    db: AsyncSession = Depends(get_db),
+):
+    """Authenticate user and return JWT access + refresh tokens."""
+    user = await authenticate_user(db, body.email, body.password)
+    if user is None:
+        raise HTTPException(
+            status_code=status.HTTP_401_UNAUTHORIZED,
+            detail={
+                "error": {
+                    "code": "INVALID_CREDENTIALS",
+                    "message": "Invalid email or password",
+                }
+            },
+        )
+    tokens = generate_token_pair(user)
+    return TokenResponse(**tokens)
+
+
+@router.post("/refresh", response_model=TokenResponse, status_code=status.HTTP_200_OK)
+async def refresh_token(
+    body: RefreshRequest,
+    db: AsyncSession = Depends(get_db),
+):
+    """Exchange a valid refresh token for a new access + refresh token pair."""
+    tokens = await refresh_access_token(db, body.refresh_token)
+    if tokens is None:
+        raise HTTPException(
+            status_code=status.HTTP_401_UNAUTHORIZED,
+            detail={
+                "error": {
+                    "code": "INVALID_REFRESH_TOKEN",
+                    "message": "Invalid or expired refresh token",
+                }
+            },
+        )
+    return TokenResponse(**tokens)
+
+
+@router.get("/me", response_model=UserResponse, status_code=status.HTTP_200_OK)
+async def get_me(current_user: User = Depends(get_current_user)):
+    """Return the currently authenticated user's profile."""
+    return UserResponse.model_validate(current_user)