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/services/OAuth2Service.ts

@@ -22,6 +22,7 @@ import {
 import { signToken, verifyToken, decodeToken, getTokenExpiresIn } from '../utils/jwt.js';
 import { verifySecret } from '../utils/crypto.js';
 import { v4 as uuidv4 } from 'uuid';
+import { tokensIssuedTotal } from '../metrics/registry.js';
 
 const FREE_TIER_MAX_MONTHLY_TOKENS = 10000;
 
@@ -202,6 +203,9 @@ export class OAuth2Service {
       { scope, expiresAt: expiresAtDate.toISOString() },
     );
 
+    // Instrument: count successful token issuances
+    tokensIssuedTotal.inc({ scope });
+
     return {
       access_token: accessToken,
       token_type: 'Bearer',