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/main.py

@@ -0,0 +1,57 @@
+"""FastAPI application entry point.
+
+Configures CORS, registers routers under /api/v1, exposes health endpoint.
+"""
+
+from contextlib import asynccontextmanager
+
+from fastapi import APIRouter, FastAPI
+from fastapi.middleware.cors import CORSMiddleware
+
+from app.config import settings
+from app.routers import auth, users
+
+
+@asynccontextmanager
+async def lifespan(app: FastAPI):
+    """Application startup and shutdown lifecycle."""
+    # Startup: could run alembic migrations here in production
+    yield
+    # Shutdown: cleanup resources
+
+
+app = FastAPI(
+    title=settings.APP_NAME,
+    description="ERP Nutzfahrzeuge Backend API",
+    version="1.0.0",
+    lifespan=lifespan,
+)
+
+# CORS configuration from settings
+app.add_middleware(
+    CORSMiddleware,
+    allow_origins=settings.cors_origins_list,
+    allow_credentials=True,
+    allow_methods=["GET", "POST", "PUT", "DELETE", "PATCH", "OPTIONS"],
+    allow_headers=["*"],
+)
+
+# API v1 router
+api_v1_router = APIRouter(prefix="/api/v1")
+api_v1_router.include_router(auth.router)
+api_v1_router.include_router(users.router)
+
+# Health endpoint (no auth required)
+@api_v1_router.get("/health", tags=["health"])
+async def health_check():
+    """Health check endpoint."""
+    return {"status": "ok"}
+
+
+app.include_router(api_v1_router)
+
+
+@app.get("/")
+async def root():
+    """Root redirect info."""
+    return {"name": settings.APP_NAME, "version": "1.0.0", "docs": "/docs"}