feat(monitoring): observability stack + app instrumentation

- /health/ready (DB+MinIO+Casdoor checks, webhook post-deploy gate),
  /metrics via prometheus-fastapi-instrumentator, Sentry/GlitchTip capture,
  X-Request-ID middleware + JSON access logging (PROCUREMENT_LOG_FORMAT)
- server-side analytics (OpenPanel Track API): login, quote lifecycle,
  receipts — fire-and-forget, disabled without env config
- monitoring/ compose project: GlitchTip(+pg), Prometheus(+alerts),
  Grafana(provisioned ERP dashboard), Loki+Promtail, node/postgres
  exporters, cAdvisor — mem-limited (~2.2GB), loopback admin UIs,
  separate from app deploys; erp_shared network for scraping
- frontend: @openpanel/web + @sentry/react (build-arg gated, no-op when
  unset), funnel events (login, wizard steps, quote submitted)
- compose: api healthcheck, observability env wiring, .env.example keys

monitoring/promtail/promtail-config.yml

@@ -0,0 +1,40 @@
+# Ships every container's JSON logs to Loki (docker service discovery),
+# tagging streams with the compose project / service / container name so
+# logs are filterable in Grafana, e.g. {compose_service="api"}.
+server:
+  http_listen_port: 9080
+
+positions:
+  filename: /tmp/positions.yaml
+
+clients:
+  - url: http://loki:3100/loki/api/v1/push
+
+scrape_configs:
+  - job_name: docker
+    docker_sd_configs:
+      - host: unix:///var/run/docker.sock
+        refresh_interval: 30s
+        filters:
+          - name: label
+            values: ["com.docker.compose.service"]
+    relabel_configs:
+      - source_labels: ["__meta_docker_container_label_com_docker_compose_project"]
+        target_label: compose_project
+      - source_labels: ["__meta_docker_container_label_com_docker_compose_service"]
+        target_label: compose_service
+      - source_labels: ["__meta_docker_container_name"]
+        target_label: container
+    pipeline_stages:
+      - json:
+          expressions:
+            ts: time
+            stream: stream
+            log: log
+      - labels:
+          stream:
+      - timestamp:
+          source: ts
+          format: RFC3339Nano
+      - output:
+          source: log