Add service health checks and dynamic Apps page

Backend polls each registered service's /health endpoint every 30 s via a
background asyncio task. GET /api/services exposes the live status snapshot.
The Apps page now renders from this endpoint — showing "Unavailable" (dimmed,
non-clickable) when a service is registered but its container is unreachable.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend/src/api/client.ts

@@ -224,6 +224,19 @@ export const updateDocumentLimits = (max_pdf_mb: number) =>
 export const getDocumentLimits = () =>
   api.get<Record<string, unknown>>("/settings/documents/limits").then((r) => r.data);
 
+// --- Services ---
+export interface ServiceStatus {
+  id: string;
+  name: string;
+  description: string;
+  healthy: boolean;
+  app_path: string;
+  settings_path: string;
+}
+
+export const getServices = () =>
+  api.get<ServiceStatus[]>("/services").then((r) => r.data);
+
 // --- System Prompts (admin only) ---
 export interface ServiceSystemPrompt {
   label: string;