Add observability: health endpoints, structured logging, metrics, Grafana stack

Health endpoints:
- /api/health (Journal) and /health (Planner) with DB connectivity check
- Docker healthchecks updated to use app health endpoints

Structured logging:
- Pino with JSON output in production, pretty-print in dev
- Request logging middleware in Planner (method, path, status, duration)
- Replaced console.log/error with structured logger in email and auth flows

Prometheus metrics:
- prom-client with default Node.js metrics + custom histograms/gauges
- /metrics endpoints on both apps
- http_request_duration, planner_active_sessions, brouter_request_duration

Monitoring stack:
- Prometheus, Loki, Grafana containers in docker-compose
- Grafana provisioned with datasources, dashboards, and alert rules
- Caddy access logging (JSON to stdout for Loki)
- grafana.trails.cool with basic auth via Caddy

Dashboards and alerting:
- Overview: request rate, error rate, latency p50/p95/p99
- Planner: active sessions, connected clients, BRouter latency
- Infrastructure: memory, CPU, event loop lag
- Alerts: disk >80%, app down 2min, error rate >5%

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

infrastructure/docker-compose.yml

@@ -29,6 +29,11 @@ services:
       SENTRY_RELEASE: ${SENTRY_RELEASE:-}
       SMTP_URL: ${SMTP_URL:-}
       SMTP_FROM: ${SMTP_FROM:-trails.cool <noreply@trails.cool>}
+    healthcheck:
+      test: ["CMD-SHELL", "curl -sf http://localhost:3000/api/health || exit 1"]
+      interval: 15s
+      timeout: 5s
+      retries: 3
     depends_on:
       postgres:
         condition: service_healthy
@@ -42,6 +47,11 @@ services:
       NODE_ENV: production
       PORT: 3001
       SENTRY_RELEASE: ${SENTRY_RELEASE:-}
+    healthcheck:
+      test: ["CMD-SHELL", "curl -sf http://localhost:3001/health || exit 1"]
+      interval: 15s
+      timeout: 5s
+      retries: 3
     depends_on:
       postgres:
         condition: service_healthy
@@ -72,6 +82,40 @@ services:
       timeout: 5s
       retries: 5
 
+  prometheus:
+    image: prom/prometheus:latest
+    restart: unless-stopped
+    volumes:
+      - ./prometheus/prometheus.yml:/etc/prometheus/prometheus.yml:ro
+      - prometheus_data:/prometheus
+    command:
+      - "--config.file=/etc/prometheus/prometheus.yml"
+      - "--storage.tsdb.retention.time=15d"
+      - "--storage.tsdb.retention.size=1GB"
+
+  loki:
+    image: grafana/loki:latest
+    restart: unless-stopped
+    volumes:
+      - ./loki/loki-config.yml:/etc/loki/local-config.yaml:ro
+      - loki_data:/loki
+    command: ["-config.file=/etc/loki/local-config.yaml"]
+
+  grafana:
+    image: grafana/grafana:latest
+    restart: unless-stopped
+    environment:
+      GF_SECURITY_ADMIN_USER: ${GRAFANA_USER:-admin}
+      GF_SECURITY_ADMIN_PASSWORD: ${GRAFANA_PASSWORD:-admin}
+      GF_SERVER_ROOT_URL: https://grafana.${DOMAIN:-trails.cool}
+    volumes:
+      - ./grafana/provisioning:/etc/grafana/provisioning:ro
+      - ./grafana/dashboards:/var/lib/grafana/dashboards:ro
+      - grafana_data:/var/lib/grafana
+    depends_on:
+      - prometheus
+      - loki
+
   # garage:
   #   image: dxflrs/garage:v1.0
   #   restart: unless-stopped
@@ -83,3 +127,6 @@ volumes:
   caddy_data:
   caddy_config:
   pgdata:
+  prometheus_data:
+  loki_data:
+  grafana_data: