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

backend/app/config.py

@@ -78,6 +78,8 @@ class Settings(BaseSettings):
     INVENTORY_DEFAULT_PROJECT_ID: str = ""
 
     # ---- Observability (Phase 2) -------------------------------------------
+    # "text" (human console) | "json" (JSON lines for Loki/Promtail).
+    LOG_FORMAT: str = "text"
     # Sentry/GlitchTip DSN — backend exception capture (empty = disabled).
     SENTRY_DSN: str = ""
     SENTRY_TRACES_SAMPLE_RATE: float = 0.0