feat(phase-3): workstream 5 — Webhooks & Event Streaming

- DB migrations 016/017: webhook_subscriptions and webhook_deliveries tables
- WebhookService: CRUD for subscriptions, Vault-backed secret storage, delivery history
- WebhookDeliveryWorker: Bull queue, HMAC-SHA256 signatures, exponential backoff,
  SSRF protection (RFC 1918 + loopback + link-local rejection), dead-letter handling
- EventPublisher: publishes 10 event types (agent/credential/token lifecycle);
  optional Kafka adapter activated via KAFKA_BROKERS env var
- AgentService, CredentialService, OAuth2Service: wired to EventPublisher
- WebhookController + routes: 6 endpoints with webhooks:read / webhooks:write scope guards
- KafkaAdapter: optional Kafka producer (kafkajs), no-op when KAFKA_BROKERS unset
- OAuthScope extended: webhooks:read, webhooks:write
- AuditAction extended: webhook.created, webhook.updated, webhook.deleted
- Metrics: agentidp_webhook_dead_letters_total counter added to registry
- 523 unit tests passing; TypeScript strict throughout, zero `any`

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

policies/data/scopes.json

@@ -24,6 +24,12 @@
     "GET:/api/v1/federation/partners":                     ["admin:orgs"],
     "GET:/api/v1/federation/partners/:id":                 ["admin:orgs"],
     "PATCH:/api/v1/federation/partners/:id":               ["admin:orgs"],
-    "DELETE:/api/v1/federation/partners/:id":              ["admin:orgs"]
+    "DELETE:/api/v1/federation/partners/:id":              ["admin:orgs"],
+    "POST:/api/v1/webhooks":                               ["webhooks:write"],
+    "GET:/api/v1/webhooks":                                ["webhooks:read"],
+    "GET:/api/v1/webhooks/:id":                            ["webhooks:read"],
+    "PATCH:/api/v1/webhooks/:id":                          ["webhooks:write"],
+    "DELETE:/api/v1/webhooks/:id":                         ["webhooks:write"],
+    "GET:/api/v1/webhooks/:id/deliveries":                 ["webhooks:read"]
   }
 }