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/config_flow.py

@@ -26,6 +26,8 @@ from .const import (
     CONF_HUB_NAME,
     CONF_IMMICH_URL,
     CONF_SCAN_INTERVAL,
+    CONF_SERVER_API_KEY,
+    CONF_SERVER_URL,
     CONF_TELEGRAM_BOT_TOKEN,
     CONF_TELEGRAM_CACHE_TTL,
     DEFAULT_SCAN_INTERVAL,
@@ -244,21 +246,40 @@ class ImmichAlbumWatcherOptionsFlow(OptionsFlow):
         self, user_input: dict[str, Any] | None = None
     ) -> ConfigFlowResult:
         """Manage the options."""
+        errors: dict[str, str] = {}
+
         if user_input is not None:
-            return self.async_create_entry(
-                title="",
-                data={
-                    CONF_SCAN_INTERVAL: user_input.get(
-                        CONF_SCAN_INTERVAL, DEFAULT_SCAN_INTERVAL
-                    ),
-                    CONF_TELEGRAM_BOT_TOKEN: user_input.get(
-                        CONF_TELEGRAM_BOT_TOKEN, ""
-                    ),
-                    CONF_TELEGRAM_CACHE_TTL: user_input.get(
-                        CONF_TELEGRAM_CACHE_TTL, DEFAULT_TELEGRAM_CACHE_TTL
-                    ),
-                },
-            )
+            # Validate server connection if URL is provided
+            server_url = user_input.get(CONF_SERVER_URL, "").strip()
+            server_api_key = user_input.get(CONF_SERVER_API_KEY, "").strip()
+            if server_url and server_api_key:
+                try:
+                    session = async_get_clientsession(self.hass)
+                    async with session.get(
+                        f"{server_url.rstrip('/')}/api/health"
+                    ) as response:
+                        if response.status != 200:
+                            errors["base"] = "server_connect_failed"
+                except Exception:
+                    errors["base"] = "server_connect_failed"
+
+            if not errors:
+                return self.async_create_entry(
+                    title="",
+                    data={
+                        CONF_SCAN_INTERVAL: user_input.get(
+                            CONF_SCAN_INTERVAL, DEFAULT_SCAN_INTERVAL
+                        ),
+                        CONF_TELEGRAM_BOT_TOKEN: user_input.get(
+                            CONF_TELEGRAM_BOT_TOKEN, ""
+                        ),
+                        CONF_TELEGRAM_CACHE_TTL: user_input.get(
+                            CONF_TELEGRAM_CACHE_TTL, DEFAULT_TELEGRAM_CACHE_TTL
+                        ),
+                        CONF_SERVER_URL: server_url,
+                        CONF_SERVER_API_KEY: server_api_key,
+                    },
+                )
 
         return self.async_show_form(
             step_id="init",
@@ -276,6 +297,12 @@ class ImmichAlbumWatcherOptionsFlow(OptionsFlow):
         current_cache_ttl = self._config_entry.options.get(
             CONF_TELEGRAM_CACHE_TTL, DEFAULT_TELEGRAM_CACHE_TTL
         )
+        current_server_url = self._config_entry.options.get(
+            CONF_SERVER_URL, ""
+        )
+        current_server_api_key = self._config_entry.options.get(
+            CONF_SERVER_API_KEY, ""
+        )
 
         return vol.Schema(
             {
@@ -288,6 +315,13 @@ class ImmichAlbumWatcherOptionsFlow(OptionsFlow):
                 vol.Optional(
                     CONF_TELEGRAM_CACHE_TTL, default=current_cache_ttl
                 ): vol.All(vol.Coerce(int), vol.Range(min=1, max=168)),
+                vol.Optional(
+                    CONF_SERVER_URL, default=current_server_url,
+                    description={"suggested_value": current_server_url},
+                ): str,
+                vol.Optional(
+                    CONF_SERVER_API_KEY, default=current_server_api_key,
+                ): str,
             }
         )