Fix journal health check and improve log collection

Switch journal Docker health check from `node -e "fetch(...)"` to `curl -sf`,
matching the planner. The Node.js process spawn was heavy and prone to timeout
under memory pressure, causing false health check failures and 502s.

Upgrade Promtail from static file scraping to Docker service discovery so logs
get `service` and `container` labels. Parse Pino JSON logs to extract the
`level` label, enabling Loki queries filtered by log level.

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

infrastructure/docker-compose.yml

@@ -35,7 +35,7 @@ services:
       WAHOO_CLIENT_SECRET: ${WAHOO_CLIENT_SECRET:-}
       WAHOO_WEBHOOK_TOKEN: ${WAHOO_WEBHOOK_TOKEN:-}
     healthcheck:
-      test: ["CMD-SHELL", "node -e \"fetch('http://localhost:3000/api/health').then(r=>{process.exit(r.ok?0:1)}).catch(()=>process.exit(1))\""]
+      test: ["CMD-SHELL", "curl -sf http://localhost:3000/api/health || exit 1"]
       interval: 15s
       timeout: 5s
       retries: 3
@@ -135,7 +135,7 @@ services:
     image: grafana/promtail:latest
     restart: unless-stopped
     volumes:
-      - /var/log:/var/log:ro
+      - /var/run/docker.sock:/var/run/docker.sock:ro
       - /var/lib/docker/containers:/var/lib/docker/containers:ro
       - ./promtail/promtail-config.yml:/etc/promtail/config.yml:ro
     command: ["-config.file=/etc/promtail/config.yml"]