feat(infra): p6 hardening - observability and deploy compose

- 5 NestJS services add /metrics endpoint via app.getHttpAdapter()
- prometheus.yml scales to 8 services with rule_files and alertmanager
- monitoring compose replaces blackbox with Loki+Promtail
- Grafana datasource adds Loki
- docker-compose.deploy.yml scales to 11 services
- deploy.env.example completes Neo4j/ES/ClickHouse/LLM vars
- teacher-bff adds health.controller
- CI removes continue-on-error on lint step
- teacher-portal lint script changed to eslint src

infra/grafana/provisioning/datasources/prometheus.yml

@@ -13,3 +13,12 @@ datasources:
       timeInterval: "15s"
       httpMethod: POST
       manageAlerts: false
+
+  - name: Loki
+    type: loki
+    uid: loki
+    access: proxy
+    url: http://loki:3100
+    editable: false
+    jsonData:
+      maxLines: 1000