Feature: Gasthund-Zugang für Sitter

- sitting_subscriptions Tabelle (dog_id, owner_id, sitter_id, valid_until)
- POST/DELETE/GET /api/sitting-access — Zugang gewähren/widerrufen/auflisten
- GET /api/dogs gibt Gasthunde zurück (is_guest=True, sitting_until, owner_name)
- Diary POST erlaubt Sitter-Schreibzugang; PATCH/DELETE nur für Besitzer
- Dog-Switcher: GAST-Badge bei fremden Hunden
- Dog-Profil: Sitter-Zugang-Sektion (nur für Besitzer), Freund auswählen + Datum
- Diary Detail-View: Bearbeiten-Button für Gasthunde ausgeblendet

backend/main.py

@@ -95,6 +95,7 @@ from routes.widget         import router as widget_router
 from routes.notifications  import router as notifications_router
 from routes.services       import router as services_router
 from routes.ratings        import router as ratings_router
+from routes.sitting_access import router as sitting_access_router
 
 app.include_router(auth_router,       prefix="/api/auth",       tags=["Auth"])
 app.include_router(dogs_router,       prefix="/api/dogs",       tags=["Hunde"])
@@ -127,6 +128,7 @@ app.include_router(widget_router,          prefix="/api/widget",  tags=["Widget"
 app.include_router(notifications_router,   prefix="/api/notifications", tags=["Notifications"])
 app.include_router(services_router,        prefix="/api/services",      tags=["Services"])
 app.include_router(ratings_router,         prefix="/api/ratings",       tags=["Ratings"])
+app.include_router(sitting_access_router,  prefix="/api/sitting-access", tags=["SittingAccess"])
 
 
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