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>

packages/shared-billing/src/models/subscription.model.ts

@@ -0,0 +1,35 @@
+import { z } from 'zod';
+import { SubscriptionTier } from '../config/billing.config';
+
+export const SubscriptionModel = z.object({
+  id: z.string(),
+  userId: z.string(),
+  stripeSubscriptionId: z.string(),
+  stripeCustomerId: z.string(),
+  tier: z.nativeEnum(SubscriptionTier),
+  status: z.enum(['active', 'canceled', 'in_trial', 'past_due', 'unpaid', 'incomplete']),
+  currentPeriodStart: z.date(),
+  currentPeriodEnd: z.date(),
+  cancelAtPeriodEnd: z.boolean().default(false),
+  createdAt: z.date(),
+  updatedAt: z.date(),
+});
+
+export type Subscription = z.infer<typeof SubscriptionModel>;
+
+export const SubscriptionCreateSchema = z.object({
+  userId: z.string(),
+  tier: z.nativeEnum(SubscriptionTier),
+  stripeCustomerId: z.string(),
+  stripeSubscriptionId: z.string(),
+  currentPeriodStart: z.date(),
+  currentPeriodEnd: z.date(),
+});
+
+export const SubscriptionUpdateSchema = z.object({
+  tier: z.nativeEnum(SubscriptionTier).optional(),
+  status: z.enum(['active', 'canceled', 'in_trial', 'past_due', 'unpaid', 'incomplete']).optional(),
+  cancelAtPeriodEnd: z.boolean().optional(),
+  currentPeriodStart: z.date().optional(),
+  currentPeriodEnd: z.date().optional(),
+});