feat(api): implement GDPR-compliant user data deletion

- Add deletedAt/deletionScheduledAt fields to User model with indexes
- Implement 5 CQRS command handlers:
  - RequestUserDeletion: 30-day soft-delete grace period
  - CancelUserDeletion: restore within grace period
  - ForceDeleteUser: admin immediate deletion with PII anonymization
  - ProcessScheduledDeletions: cron-ready batch processor
  - ExportUserData: GDPR Article 20 data portability
- Cascade strategy: anonymize PII, expire listings, cancel subscriptions,
  delete reviews/inquiries/searches/notifications, preserve payments for audit
- Add UserDataController with DELETE /users/me, POST /users/me/cancel-deletion,
  GET /users/me/export, DELETE /users/:id/force (admin)
- 22 unit tests covering all handlers (160 files, 853 tests passing)
- Migration: 20260410000000_add_user_soft_delete_fields

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

prisma/migrations/20260410000000_add_user_soft_delete_fields/migration.sql

@@ -0,0 +1,9 @@
+-- AlterTable
+ALTER TABLE "User" ADD COLUMN "deletedAt" TIMESTAMP(3),
+ADD COLUMN "deletionScheduledAt" TIMESTAMP(3);
+
+-- CreateIndex
+CREATE INDEX "User_deletedAt_idx" ON "User"("deletedAt");
+
+-- CreateIndex
+CREATE INDEX "User_deletionScheduledAt_idx" ON "User"("deletionScheduledAt");