Sprint 13: WebCal-Abo / Kalender-Integration

- GET /api/webcal/token: erzeugt personl. Kalender-Token (einmalig)
- GET /api/webcal/{token}.ics: iCal-Feed mit Health-Erinnerungen,
  eigenen Events, Gassi-Treffen (erstellt + beigetreten), angenommenen Sittings
- RRULE für wiederkehrende Health-Einträge (intervall_tage)
- Migration: users.calendar_token (TEXT UNIQUE)
- Settings: "Kalender abonnieren" öffnet webcal://-Link + Kopier-Button
- api.js: API.webcal.getToken() / resetToken()
- SW-Cache: by-v104, APP_VER: 80

backend/main.py

@@ -71,6 +71,7 @@ from routes.movies     import router as movies_router
 from routes.friends    import router as friends_router
 from routes.chat       import router as chat_router
 from routes.admin      import router as admin_router
+from routes.webcal     import router as webcal_router
 
 app.include_router(auth_router,       prefix="/api/auth",       tags=["Auth"])
 app.include_router(dogs_router,       prefix="/api/dogs",       tags=["Hunde"])
@@ -94,6 +95,7 @@ app.include_router(movies_router,     prefix="/api/movies",     tags=["Filme"])
 app.include_router(friends_router,    prefix="/api/friends",    tags=["Freunde"])
 app.include_router(chat_router,       prefix="/api/chat",       tags=["Chat"])
 app.include_router(admin_router,      prefix="/api/admin",      tags=["Admin"])
+app.include_router(webcal_router,     prefix="/api/webcal",     tags=["WebCal"])
 
 
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