feat(offline): persisted query cache + unreachable banner (web + mobile) (#70)

* feat(offline): persisted query cache + unreachable banner (web + mobile)

- Web: PersistQueryClientProvider on localStorage (24h maxAge); mobile:
  AsyncStorage persister (7d). Both exclude high-churn keys (logs,
  notifications, metrics) — stale tails are worse than none.
- networkMode 'offlineFirst' so cached data serves while the refetch
  attempt fails.
- Web: ConnectivityBanner in PlatformShell pings public /health every
  15s + listens to online/offline events — slim "last-known data" bar
  so persisted state can't masquerade as live.
- Mobile: same banner in the tabs layout — /health ping plus
  expo-network's local signal distinguishes "no connection" from
  "instance down".

Generated with [Devin](https://devin.ai)

Co-Authored-By: Devin <158243242+devin-ai-integration[bot]@users.noreply.github.com>

* feat(mobile): cron jobs screen — schedules, run-now, execution history

- /service/cron lists the service's jobs with schedule, timezone,
  last/next run, and last status; "Run now" triggers via the existing
  POST /cron-jobs/:id/trigger and "History" expands recent executions
  with status + output/error.
- Manage row on the service detail + Stack registration.

Verified live: created */5 job on a running service, triggered it —
execution recorded with status success and captured stdout.

Generated with [Devin](https://devin.ai)

Co-Authored-By: Devin <158243242+devin-ai-integration[bot]@users.noreply.github.com>

---------

Co-authored-by: Devin <158243242+devin-ai-integration[bot]@users.noreply.github.com>

app/frontend/src/lib/api-client.ts

@@ -490,6 +490,15 @@ export function getApiBaseUrl(): string {
   return API_BASE;
 }
 
+// pingServer hits the public /health route — any HTTP response proves
+// reachability, and no auth means no 401 noise in the connectivity probe.
+export async function pingServer(): Promise<void> {
+  const res = await fetch(`${API_ROOT}/health`);
+  if (!res.ok) {
+    throw new Error(`Server returned ${res.status}`);
+  }
+}
+
 export function getAgentPublicBaseUrl(): string {
   return `${API_ROOT}/api/agents`;
 }