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/backend/src/tracing.js

@@ -9,8 +9,10 @@
 // routed to Tempo.
 
 import { NodeSDK } from '@opentelemetry/sdk-node';
+import { PeriodicExportingMetricReader } from '@opentelemetry/sdk-metrics';
 import { getNodeAutoInstrumentations } from '@opentelemetry/auto-instrumentations-node';
 import { OTLPTraceExporter } from '@opentelemetry/exporter-trace-otlp-grpc';
+import { OTLPMetricExporter } from '@opentelemetry/exporter-metrics-otlp-grpc';
 import * as resources from '@opentelemetry/resources';
 import { ATTR_SERVICE_NAME, ATTR_SERVICE_NAMESPACE } from '@opentelemetry/semantic-conventions';
 import { PinoInstrumentation } from '@opentelemetry/instrumentation-pino';
@@ -28,9 +30,18 @@ const resource = typeof resources.resourceFromAttributes === 'function'
       [ATTR_SERVICE_NAMESPACE]: 'farmaclic',
     });
 
+// Metrics → OTLP → Alloy → Prometheus remote_write. The PeriodicExportingMetricReader
+// makes the auto-instrumentations (http/express/redis) emit request duration/error
+// metrics with no extra code, on top of the custom business metrics in src/metrics.js.
+const metricReader = new PeriodicExportingMetricReader({
+  exportIntervalMillis: 15_000,
+  exporter: new OTLPMetricExporter({ url: otlpEndpoint }),
+});
+
 const sdk = new NodeSDK({
   resource,
   traceExporter: new OTLPTraceExporter({ url: otlpEndpoint }),
+  metricReader,
   instrumentations: [
     getNodeAutoInstrumentations({
       // Disable fs by default — it is noisy and rarely useful.