feat(subscriptions): implement subscription quota enforcement

- Apply QuotaGuard + @RequireQuota to listing creation and analytics endpoints
- Add QuotaExceeded domain event emitted when quota is exceeded
- Create ListingCreatedUsageHandler to auto-meter usage on listing creation
- Create QuotaExceededListener to send email notifications on quota exceeded
- Add maxAnalyticsQueries and maxMediaUploads fields to Plan model
- Add quota.exceeded email notification template
- Define quota limits per plan tier in seed data
- Add 15 unit tests covering guard, event handler, listener, and event

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

apps/api/src/modules/subscriptions/domain/events/quota-exceeded.event.ts

@@ -0,0 +1,13 @@
+import { type DomainEvent } from '@modules/shared/domain/domain-event';
+
+export class QuotaExceededEvent implements DomainEvent {
+  readonly eventName = 'quota.exceeded';
+  readonly occurredAt = new Date();
+
+  constructor(
+    public readonly aggregateId: string, // userId
+    public readonly metric: string,
+    public readonly limit: number,
+    public readonly used: number,
+  ) {}
+}