feat(audit): Authentik events ingest worker (Phase 2 chunk 1)

Background worker that pulls Authentik's /api/v3/events/events/ on a
60s cadence and writes each event into our audit log via AuditService.
External system events now share the same /audit timeline as
internally-recorded platform mutations — operator queries don't have
to cross-reference Authentik's own UI to see logins, password changes,
group membership, impersonation, etc.

Pieces:
- src/schemas/ingest-cursor.schema.ts: one row per source, tracks
  lastEventAt + lastEventId so restarts resume without re-pulling.
- src/schemas/audit-event.schema.ts: new `externalId` field; new
  compound unique index on (source, externalId) with a partial filter
  on externalId being a string. Partial (not sparse) so internally-
  recorded events with externalId=null don't collide.
- src/audit/audit.service.ts: AuditRecordInput grows `externalId` +
  `at` fields. record() now silently swallows MongoError code 11000
  (duplicate key) so re-pulling the cursor overlap doesn't log noise.
- src/integrations/authentik.client.ts: listEvents(since, page,
  pageSize) on the existing client — reuses the admin token and base
  URL the provisioning code already configured.
- src/ingest/action-map.ts: 16 known Authentik actions → dotted
  authentik.* verbs (login, login_failed, password_changed,
  impersonation_started, …). Unknown actions fall through to
  authentik.<raw> rather than getting silently dropped.
- src/ingest/authentik.ingest.ts: OnApplicationBootstrap worker.
  Reads cursor → pulls events with created__gt=cursor, ordering=created
  ASC → paginates forward (10 pages × 100/page safety cap per tick) →
  writes each event with source='authentik' + externalId=pk + at=
  evt.created → advances cursor to the newest seen. inFlight guard
  prevents overlapping ticks. AUDIT_INGEST_ENABLED=false disables for
  test environments.
- Tenant inference: from the user's groups (same convention the portal
  flag-eval proxy uses). Admin groups stripped; first match against a
  real Tenant.slug wins. Unmatched → tenantSlug undefined, event still
  lands in the global timeline.

Smoke-tested: fresh Mongo + restart → 78 Authentik events ingested,
0 duplicates. Performed a login at app.dezky.local → next 60s tick
captured the new login row with actor email + IP. Compound unique
index on (source, externalId) verified to reject re-pulled events
silently (no error logs).

Out of scope here (covered by chunks 2 + 3):
- Stalwart webhook ingest
- OCIS file-tail ingest

services/platform-api/src/ingest/ingest.module.ts

@@ -0,0 +1,26 @@
+import { Module } from '@nestjs/common'
+import { MongooseModule } from '@nestjs/mongoose'
+import { AuditModule } from '../audit/audit.module.js'
+import { IntegrationsModule } from '../integrations/integrations.module.js'
+import {
+  IngestCursor,
+  IngestCursorSchema,
+} from '../schemas/ingest-cursor.schema.js'
+import { Tenant, TenantSchema } from '../schemas/tenant.schema.js'
+import { AuthentikIngest } from './authentik.ingest.js'
+
+// Workers that pull audit events from external systems (Authentik today,
+// Stalwart + OCIS later) and forward them to AuditService. Each worker owns
+// its own cursor in the ingest_cursors collection so restarts resume cleanly.
+@Module({
+  imports: [
+    AuditModule,
+    IntegrationsModule,
+    MongooseModule.forFeature([
+      { name: IngestCursor.name, schema: IngestCursorSchema },
+      { name: Tenant.name, schema: TenantSchema },
+    ]),
+  ],
+  providers: [AuthentikIngest],
+})
+export class IngestModule {}