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>

plans/primary-plan.md

@@ -200,7 +200,7 @@ async def _execute_telegram_notification(self, ...):
 - Album picker connected to Immich API
 - **Subplan**: `plans/phase-4-frontend.md`
 
-### Phase 5: HAOS-Server Sync (Optional) `[ ]`
+### Phase 5: HAOS-Server Sync (Optional) `[x]`
 - Add optional server URL to HA config flow
 - Implement tracker/template config sync
 - **Subplan**: `plans/phase-5-haos-server-sync.md`