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/__tests__/quota-exceeded.event.spec.ts

@@ -0,0 +1,21 @@
+import { QuotaExceededEvent } from '../events/quota-exceeded.event';
+
+describe('QuotaExceededEvent', () => {
+  it('creates event with correct properties', () => {
+    const event = new QuotaExceededEvent('user-1', 'listings_created', 3, 3);
+
+    expect(event.eventName).toBe('quota.exceeded');
+    expect(event.aggregateId).toBe('user-1');
+    expect(event.metric).toBe('listings_created');
+    expect(event.limit).toBe(3);
+    expect(event.used).toBe(3);
+    expect(event.occurredAt).toBeInstanceOf(Date);
+  });
+
+  it('creates event for analytics metric', () => {
+    const event = new QuotaExceededEvent('user-2', 'analytics_queries', 0, 0);
+
+    expect(event.metric).toBe('analytics_queries');
+    expect(event.limit).toBe(0);
+  });
+});

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,
+  ) {}
+}