feat: add end-to-end observability (metrics, health, mobile RUM, dashboards, alerts)

- Backend: OTel metrics via OTLP -> Alloy -> Prometheus (OTEL_METRICS_EXPORTER=otlp)
- New business metrics (src/metrics.js): searches, CIMA latency/errors, cache
  hits/misses, logins, rate-limits, pharmacy writes/links, push sent/failed,
  DB + Redis timings/errors, HTTP req count/duration, heartbeat
- Backend health endpoints /healthz and /readyz
- Mobile (Expo): Grafana Faro RUM via @grafana/faro-react-native
- redis/postgres exporters in docker-compose + Prometheus scrape jobs
- Grafana dashboards (backend, datastores, mobile RUM, overview)
- Prometheus alert rules (farmafinder_*) -> existing Alertmanager (Telegram)
- Design/spec saved to docs/superpowers/specs/

apps/frontend-mobile/app/_layout.tsx

@@ -8,6 +8,10 @@ import { SafeAreaProvider } from 'react-native-safe-area-context';
 import { useAuthStore } from '../store/authStore';
 import { registerForPushNotifications, addNotificationListener, addNotificationResponseListener } from '../services/notifications';
 import { ThemeProvider, useThemeContext } from '../components/ThemeProvider';
+import { initFaro } from '../services/faro';
+
+// Boot Faro RUM once, as early as possible.
+initFaro();
 
 const queryClient = new QueryClient();