Fix health check loop silently dying on uncaught exception

Wrap check_all() call inside the loop with try/except so a transient error
cannot exit the while-True and freeze all health statuses. Add transition
logging (HEALTHY / UNHEALTHY) so docker logs show when a service changes
state. Also add refetchIntervalInBackground on the frontend query so the
poll continues even when the browser tab is not focused.

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

frontend/src/pages/AppsPage.tsx

@@ -32,6 +32,7 @@ export default function AppsPage() {
     queryKey: ["services"],
     queryFn: getServices,
     refetchInterval: 30_000,
+    refetchIntervalInBackground: true,
   });
 
   return (