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>

custom_components/immich_album_watcher/sync.py

@@ -0,0 +1,123 @@
+"""Optional sync with the standalone Immich Watcher server."""
+
+from __future__ import annotations
+
+import logging
+from typing import Any
+
+import aiohttp
+
+from homeassistant.core import HomeAssistant
+from homeassistant.helpers.aiohttp_client import async_get_clientsession
+
+_LOGGER = logging.getLogger(__name__)
+
+
+class ServerSyncClient:
+    """Client for communicating with the standalone Immich Watcher server.
+
+    All methods are safe to call even if the server is unreachable --
+    they log warnings and return empty/default values. The HA integration
+    must never break due to server connectivity issues.
+    """
+
+    def __init__(self, hass: HomeAssistant, server_url: str, api_key: str) -> None:
+        self._hass = hass
+        self._base_url = server_url.rstrip("/")
+        self._api_key = api_key
+
+    @property
+    def _headers(self) -> dict[str, str]:
+        return {"X-API-Key": self._api_key, "Content-Type": "application/json"}
+
+    async def async_get_trackers(self) -> list[dict[str, Any]]:
+        """Fetch tracker configurations from the server.
+
+        Returns empty list on any error.
+        """
+        try:
+            session = async_get_clientsession(self._hass)
+            async with session.get(
+                f"{self._base_url}/api/sync/trackers",
+                headers=self._headers,
+            ) as response:
+                if response.status == 200:
+                    return await response.json()
+                _LOGGER.warning(
+                    "Server sync: failed to fetch trackers (HTTP %d)", response.status
+                )
+        except aiohttp.ClientError as err:
+            _LOGGER.warning("Server sync: connection failed: %s", err)
+        return []
+
+    async def async_render_template(
+        self, template_id: int, context: dict[str, Any]
+    ) -> str | None:
+        """Render a server-managed template with context.
+
+        Returns None on any error.
+        """
+        try:
+            session = async_get_clientsession(self._hass)
+            async with session.post(
+                f"{self._base_url}/api/sync/templates/{template_id}/render",
+                headers=self._headers,
+                json={"context": context},
+            ) as response:
+                if response.status == 200:
+                    data = await response.json()
+                    return data.get("rendered")
+                _LOGGER.warning(
+                    "Server sync: template render failed (HTTP %d)", response.status
+                )
+        except aiohttp.ClientError as err:
+            _LOGGER.warning("Server sync: template render connection failed: %s", err)
+        return None
+
+    async def async_report_event(
+        self,
+        tracker_name: str,
+        event_type: str,
+        album_id: str,
+        album_name: str,
+        details: dict[str, Any] | None = None,
+    ) -> bool:
+        """Report a detected event to the server for logging.
+
+        Returns True if successfully reported, False on any error.
+        Fire-and-forget -- failures are logged but don't affect HA operation.
+        """
+        try:
+            session = async_get_clientsession(self._hass)
+            payload = {
+                "tracker_name": tracker_name,
+                "event_type": event_type,
+                "album_id": album_id,
+                "album_name": album_name,
+                "details": details or {},
+            }
+            async with session.post(
+                f"{self._base_url}/api/sync/events",
+                headers=self._headers,
+                json=payload,
+            ) as response:
+                if response.status == 200:
+                    _LOGGER.debug("Server sync: event reported for album '%s'", album_name)
+                    return True
+                _LOGGER.debug(
+                    "Server sync: event report failed (HTTP %d)", response.status
+                )
+        except aiohttp.ClientError as err:
+            _LOGGER.debug("Server sync: event report connection failed: %s", err)
+        return False
+
+    async def async_check_connection(self) -> bool:
+        """Check if the server is reachable."""
+        try:
+            session = async_get_clientsession(self._hass)
+            async with session.get(
+                f"{self._base_url}/api/health",
+            ) as response:
+                return response.status == 200
+        except aiohttp.ClientError:
+            return False