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/prometheus/alerts.yml

@@ -0,0 +1,58 @@
+# Alert rules surfaced in Grafana's alerting UI (no Alertmanager needed at
+# this scale — Grafana can route them later via email/Telegram).
+groups:
+  - name: erp-availability
+    rules:
+      - alert: ErpApiDown
+        expr: up{job="erp-api"} == 0
+        for: 2m
+        labels:
+          severity: critical
+        annotations:
+          summary: "ERP API is not scraping (down or /metrics failing)"
+
+      - alert: ErpApiHighErrorRate
+        expr: |
+          sum(rate(http_requests_total{job="erp-api", status=~"5.."}[5m]))
+            / clamp_min(sum(rate(http_requests_total{job="erp-api"}[5m])), 0.001) > 0.05
+        for: 5m
+        labels:
+          severity: warning
+        annotations:
+          summary: "ERP API 5xx rate above 5% for 5 minutes"
+
+      - alert: ErpApiSlowRequests
+        expr: |
+          histogram_quantile(0.95,
+            sum(rate(http_request_duration_seconds_bucket{job="erp-api"}[5m])) by (le)) > 2
+        for: 10m
+        labels:
+          severity: warning
+        annotations:
+          summary: "ERP API p95 latency above 2s for 10 minutes"
+
+  - name: host
+    rules:
+      - alert: HostDiskAlmostFull
+        expr: (node_filesystem_avail_bytes{mountpoint="/", fstype!~"tmpfs|overlay"} / node_filesystem_size_bytes{mountpoint="/", fstype!~"tmpfs|overlay"}) < 0.1
+        for: 15m
+        labels:
+          severity: critical
+        annotations:
+          summary: "Root filesystem below 10% free (deploy builds will fail)"
+
+      - alert: HostMemoryPressure
+        expr: node_memory_MemAvailable_bytes / node_memory_MemTotal_bytes < 0.1
+        for: 10m
+        labels:
+          severity: warning
+        annotations:
+          summary: "Host RAM below 10% available (check monitoring stack limits)"
+
+      - alert: PostgresTooManyConnections
+        expr: sum(pg_stat_activity_count) > 80
+        for: 10m
+        labels:
+          severity: warning
+        annotations:
+          summary: "PostgreSQL connection count above 80"