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/metrics/registry.ts

@@ -0,0 +1,79 @@
+/**
+ * Shared Prometheus metrics registry for SentryAgent.ai AgentIdP.
+ * All 7 metric definitions live here. Import specific metrics in the files that use them.
+ * This is the ONLY file that defines metrics — all other files import from here.
+ */
+
+import { Registry, Counter, Histogram } from 'prom-client';
+
+/** Shared registry — do NOT use the default global registry (conflicts with tests). */
+export const metricsRegistry = new Registry();
+
+/**
+ * Total number of OAuth 2.0 tokens successfully issued.
+ * Labels: scope (space-separated scope string)
+ */
+export const tokensIssuedTotal = new Counter({
+  name: 'agentidp_tokens_issued_total',
+  help: 'Total number of OAuth 2.0 access tokens issued successfully.',
+  labelNames: ['scope'] as const,
+  registers: [metricsRegistry],
+});
+
+/**
+ * Total number of agents successfully registered.
+ * Labels: deployment_env
+ */
+export const agentsRegisteredTotal = new Counter({
+  name: 'agentidp_agents_registered_total',
+  help: 'Total number of AI agents registered successfully.',
+  labelNames: ['deployment_env'] as const,
+  registers: [metricsRegistry],
+});
+
+/**
+ * Total HTTP requests received.
+ * Labels: method, route (normalised path), status_code
+ */
+export const httpRequestsTotal = new Counter({
+  name: 'agentidp_http_requests_total',
+  help: 'Total number of HTTP requests received.',
+  labelNames: ['method', 'route', 'status_code'] as const,
+  registers: [metricsRegistry],
+});
+
+/**
+ * HTTP request duration in seconds.
+ * Labels: method, route, status_code
+ */
+export const httpRequestDurationSeconds = new Histogram({
+  name: 'agentidp_http_request_duration_seconds',
+  help: 'HTTP request duration in seconds.',
+  labelNames: ['method', 'route', 'status_code'] as const,
+  buckets: [0.005, 0.01, 0.025, 0.05, 0.1, 0.25, 0.5, 1, 2.5],
+  registers: [metricsRegistry],
+});
+
+/**
+ * PostgreSQL query duration in seconds.
+ * Labels: operation (query/connect)
+ */
+export const dbQueryDurationSeconds = new Histogram({
+  name: 'agentidp_db_query_duration_seconds',
+  help: 'PostgreSQL query duration in seconds.',
+  labelNames: ['operation'] as const,
+  buckets: [0.001, 0.005, 0.01, 0.025, 0.05, 0.1, 0.25, 0.5, 1],
+  registers: [metricsRegistry],
+});
+
+/**
+ * Redis command duration in seconds.
+ * Labels: command (get/set/incr/expire/ping/etc.)
+ */
+export const redisCommandDurationSeconds = new Histogram({
+  name: 'agentidp_redis_command_duration_seconds',
+  help: 'Redis command duration in seconds.',
+  labelNames: ['command'] as const,
+  buckets: [0.0005, 0.001, 0.005, 0.01, 0.025, 0.05, 0.1, 0.25],
+  registers: [metricsRegistry],
+});