feat(phase-2): workstream 7 — Prometheus + Grafana Monitoring

- Add prom-client 15; shared registry in src/metrics/registry.ts (7 metrics)
- HTTP request counter + duration histogram via metricsMiddleware
- DB query duration histogram wrapping pg Pool.query
- Redis command duration histogram via typed instrumentRedisMethod wrapper
- agentidp_tokens_issued_total in OAuth2Service
- agentidp_agents_registered_total in AgentService
- GET /metrics unauthenticated endpoint (Prometheus text format)
- docker-compose.monitoring.yml overlay (Prometheus + Grafana)
- Grafana auto-provisioned datasource + pre-built AgentIdP dashboard
- docs/devops/operations.md monitoring section added
- 36/36 unit tests passing, 100% coverage on new metrics code
- Fix pre-existing unused import in tests/integration/agents.test.ts

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/db/pool.ts

@@ -4,6 +4,7 @@
  */
 
 import { Pool } from 'pg';
+import { dbQueryDurationSeconds } from '../metrics/registry.js';
 
 let pool: Pool | null = null;
 
@@ -26,6 +27,24 @@ export function getPool(): Pool {
       // eslint-disable-next-line no-console
       console.error('Unexpected pg pool error', err);
     });
+
+    // Wrap pool.query to record duration in Prometheus.
+    // The pg Pool.query method is heavily overloaded — the only safe approach
+    // without TypeScript errors is a typed-any wrapper on the shim itself.
+    // We capture originalQuery as `(...args: any[]) => Promise<any>` to satisfy
+    // TypeScript's spread-into-rest constraint; this is the one sanctioned use of
+    // `any` in this file.
+    // eslint-disable-next-line @typescript-eslint/no-explicit-any
+    const originalQuery = pool.query.bind(pool) as (...args: any[]) => Promise<any>;
+    // eslint-disable-next-line @typescript-eslint/no-explicit-any
+    (pool as any).query = async (...args: any[]): Promise<any> => {
+      const end = dbQueryDurationSeconds.startTimer({ operation: 'query' });
+      try {
+        return await originalQuery(...args);
+      } finally {
+        end();
+      }
+    };
   }
   return pool;
 }