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/integrations/authentik.client.ts

@@ -69,4 +69,37 @@ export class AuthentikClient {
     }
     this.logger.log(`Deleted Authentik group ${groupId}`)
   }
+
+  // Pull a window of Authentik events. Used by the audit ingest worker.
+  // `since` filters by created timestamp (strict greater-than); pagination is
+  // forward-only via `page`. Authentik's default page size is 100.
+  async listEvents(
+    since?: Date,
+    page = 1,
+    pageSize = 100,
+  ): Promise<AuthentikEventPage> {
+    const params = new URLSearchParams({
+      ordering: 'created',
+      page: String(page),
+      page_size: String(pageSize),
+    })
+    if (since) params.set('created__gt', since.toISOString())
+    return this.request<AuthentikEventPage>(`/events/events/?${params}`)
+  }
+}
+
+// Shape returned by /events/events/. Only the fields we read; Authentik
+// includes a number of others (tenant, brand) we don't need.
+export interface AuthentikEvent {
+  pk: string
+  action: string
+  app?: string
+  user?: { pk?: number; username?: string; name?: string; email?: string }
+  context?: Record<string, unknown>
+  client_ip?: string
+  created: string
+}
+export interface AuthentikEventPage {
+  pagination: { next: number; previous: number; count: number; current: number; total_pages: number; start_index: number; end_index: number }
+  results: AuthentikEvent[]
 }