Lokale Kalender und iCal-URL-Abonnements

Neue Features:
- Lokale Kalender erstellen mit vollem Event-CRUD (in SQLite gespeichert)
- iCal-URLs abonnieren mit Auto-Refresh und lokalem Caching
- iCal-Events sind editierbar/löschbar (Änderungen als lokale Overrides)
- Sidebar zeigt alle 3 Kalendertypen mit Farbe, Umbenennen, Löschen
- Dropdown "Kalender hinzufügen" mit 3 Optionen (Lokal, CalDAV, iCal)
Backend: models.py (4 neue Tabellen), local_router.py, ical_router.py
Frontend: Neue Modals, erweiterte Sidebar, Source-basiertes Event-Routing

backend/main.py

@@ -12,7 +12,7 @@ from sqlalchemy import text
 sys.path.insert(0, str(Path(__file__).parent))
 
 from database import Base, engine
-from routers import auth_router, caldav_router, profile_router, settings_router, users_router
+from routers import auth_router, caldav_router, ical_router, local_router, profile_router, settings_router, users_router
 
 logging.basicConfig(level=logging.INFO)
 
@@ -41,6 +41,8 @@ app.include_router(users_router.router, prefix="/api/users", tags=["users"])
 app.include_router(caldav_router.router, prefix="/api/caldav", tags=["caldav"])
 app.include_router(settings_router.router, prefix="/api/settings", tags=["settings"])
 app.include_router(profile_router.router, prefix="/api/profile", tags=["profile"])
+app.include_router(local_router.router, prefix="/api/local", tags=["local"])
+app.include_router(ical_router.router, prefix="/api/ical", tags=["ical"])
 
 FRONTEND_DIR = Path(__file__).parent.parent / "frontend"
 app.mount("/static", StaticFiles(directory=str(FRONTEND_DIR)), name="static")