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>

prisma/schema.prisma

@@ -423,9 +423,11 @@ model Plan {
   name             String
   priceMonthlyVND  BigInt
   priceYearlyVND   BigInt
-  maxListings      Int?
-  maxSavedSearches Int?
-  features         Json
+  maxListings         Int?
+  maxSavedSearches   Int?
+  maxAnalyticsQueries Int?
+  maxMediaUploads    Int?
+  features           Json
   isActive         Boolean  @default(true)
 
   subscriptions Subscription[]