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/migrations/20260408080000_add_analytics_media_quota_fields/migration.sql

@@ -0,0 +1,3 @@
+-- AlterTable
+ALTER TABLE "Plan" ADD COLUMN "maxAnalyticsQueries" INTEGER;
+ALTER TABLE "Plan" ADD COLUMN "maxMediaUploads" INTEGER;