feat: Actions system — scheduled mutations on external services

Full-stack implementation of provider-scoped Actions with extensible
executor architecture. First action type: Immich auto_organize (sort
assets into albums by person, CLIP search, date range, favorites).

Core:
- ActionTypeDefinition registry + ActionExecutor ABC with execute/validate/dry-run
- ImmichActionExecutor with multi-album support and client-side filtering
- ImmichClient write methods: add/remove assets, create album, paginated search

Server:
- Action, ActionRule, ActionExecution DB models
- Full CRUD API + manual execute + dry-run + execution history endpoints
- APScheduler integration (interval + cron) for automated execution
- Action type discovery API + provider people endpoint

Frontend:
- Actions page with CRUD, execute/dry-run buttons, inline rule editor
- RuleEditor: person/album MultiEntitySelect pickers, criteria config
- ExecutionHistory: expandable per-rule result details
- MultiEntitySelect reusable component (searchable multi-pick palette)
- Notification tracker album picker migrated to MultiEntitySelect
- Fixed MdiIcon race condition (icons missing after cache-clearing reload)

packages/server/src/notify_bridge_server/api/providers.py

@@ -193,6 +193,7 @@ async def list_provider_capabilities():
             "commands": caps.commands,
             "supported_filters": caps.supported_filters,
             "webhook_based": caps.webhook_based,
+            "action_types": caps.action_types,
         }
     return result
 
@@ -351,6 +352,29 @@ async def test_provider(
     return {"ok": False, "message": f"Unknown provider type: {provider.type}"}
 
 
+@router.get("/{provider_id}/people")
+async def list_people(
+    provider_id: int,
+    user: User = Depends(get_current_user),
+    session: AsyncSession = Depends(get_session),
+):
+    """Fetch people from a service provider (Immich only)."""
+    provider = await _get_user_provider(session, provider_id, user.id)
+
+    if provider.type == "immich":
+        from notify_bridge_core.providers.immich.client import ImmichClient
+        async with aiohttp.ClientSession() as http_session:
+            client = ImmichClient(
+                http_session,
+                provider.config.get("url", ""),
+                provider.config.get("api_key", ""),
+            )
+            people_dict = await client.get_people()
+            return [{"id": pid, "name": name} for pid, name in people_dict.items()]
+
+    return []
+
+
 @router.get("/{provider_id}/collections")
 async def list_collections(
     provider_id: int,