Add HAOS-Server sync for optional centralized management (Phase 5)

Enable the HAOS integration to optionally connect to the standalone
Immich Watcher server for config sync and event reporting.

Server-side:
- New /api/sync/* endpoints: GET trackers, POST template render,
  POST event report
- API key auth via X-API-Key header (accepts JWT access tokens)

Integration-side:
- New sync.py: ServerSyncClient with graceful error handling
  (all methods return defaults on connection failure)
- Options flow: optional server_url and server_api_key fields
  with connection validation
- Coordinator: fire-and-forget event reporting to server when
  album changes are detected
- Translations: en.json and ru.json updated with new fields

The connection is fully additive -- the integration works identically
without a server URL configured. Server failures never break HA.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

packages/server/src/immich_watcher_server/main.py

@@ -21,6 +21,7 @@ from .api.templates import router as templates_router
 from .api.targets import router as targets_router
 from .api.users import router as users_router
 from .api.status import router as status_router
+from .api.sync import router as sync_router
 
 logging.basicConfig(
     level=logging.DEBUG if settings.debug else logging.INFO,
@@ -69,6 +70,7 @@ app.include_router(templates_router)
 app.include_router(targets_router)
 app.include_router(users_router)
 app.include_router(status_router)
+app.include_router(sync_router)
 
 # Serve frontend static files if available
 _frontend_dist = Path(__file__).parent / "frontend"