Add tier-based scan scheduler and webhook triggers (FRE-4498)

- ScanScheduler: tier-based scheduling (BASIC=24h, PLUS=6h, PREMIUM=1h)
- WebhookHandler: HMAC-verified webhook ingestion with SCAN_TRIGGER support
- API routes: /scheduler and /webhooks endpoints under /api/v1/darkwatch
- Jobs: scheduled scan checker + webhook retry processor via BullMQ
- Schema: ScanSchedule, WebhookEvent models; ScanJob.scheduledBy field
- Types: ScheduleStatus, WebhookEventType, WebhookTriggerInput
- Tests: scheduler lifecycle + webhook signature/processing tests

Co-Authored-By: Paperclip <noreply@paperclip.ing>

.env.prod.example

@@ -0,0 +1,13 @@
+# Database
+POSTGRES_PASSWORD=change_me_in_production
+
+# API Keys
+HIBP_API_KEY=""
+RESEND_API_KEY=""
+
+# Docker (for deployment)
+DOCKER_TAG=latest
+GITHUB_REPOSITORY_OWNER=shieldai
+
+# Server
+PORT=3000