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>

services/spamshield/package.json

@@ -0,0 +1,22 @@
+{
+  "name": "@shieldai/spamshield",
+  "version": "0.1.0",
+  "main": "./dist/index.js",
+  "types": "./dist/index.d.ts",
+  "scripts": {
+    "build": "tsc",
+    "dev": "tsx watch src/index.ts",
+    "lint": "eslint src/",
+    "typecheck": "tsc --noEmit"
+  },
+  "dependencies": {
+    "@shieldai/db": "0.1.0",
+    "@prisma/client": "^6.2.0",
+    "libphonenumber-js": "^1.10.50"
+  },
+  "devDependencies": {
+    "typescript": "^5.3.3",
+    "tsx": "^4.19.0",
+    "eslint": "^8.56.0"
+  }
+}