feat(audit): add comprehensive audit logging with SIEM integration

- Add AuditLog model with append-only design (timestamp, user, action, resource, IP, details, severity)
- Add audit_service.py with record/query helpers and SIEM forwarding (Syslog RFC 5424, HTTP/webhook)
- Add /api/audit-logs REST endpoints with filtering and pagination
- Add /admin/audit-logs viewer UI with real-time filters
- Add SIEM config settings (syslog, HTTP for Splunk HEC/Logstash/Grafana Loki)
- Add Alembic migration 027_add_audit_logs
- Add navigation link in admin menu
- Add comprehensive tests (20 tests covering model, service, SIEM, API, view)

Co-authored-by: christianlouis <361235+christianlouis@users.noreply.github.com>

app/api/__init__.py

@@ -8,6 +8,7 @@ from fastapi import APIRouter
 
 from app.api.admin_users import router as admin_users_router
 from app.api.api_tokens import router as api_tokens_router
+from app.api.audit_logs import router as audit_logs_router
 from app.api.azure import router as azure_router
 from app.api.backup import router as backup_router
 from app.api.billing import router as billing_router
@@ -82,3 +83,4 @@ router.include_router(imap_accounts_router)
 router.include_router(integrations_router)
 router.include_router(notifications_router)
 router.include_router(scheduled_jobs_router)
+router.include_router(audit_logs_router)