feat(db): implement complete database schema and models

- Add Prisma schema with PostgreSQL 15 support
- Create Users, Batches, Images, Payments, ApiKeys tables
- Implement proper foreign key relationships and indexes
- Add enum types for status fields (Plan, BatchStatus, ImageStatus, PaymentStatus)
- Support for JSON fields (vision_tags, metadata)
- UUID primary keys for security
- Created/updated timestamps with proper defaults

Database Layer Components:
- Prisma service with connection management and health checks
- Repository pattern for all entities with comprehensive CRUD operations
- TypeScript DTOs with class-validator decorations
- Swagger API documentation annotations
- Helper functions for business logic (quota management, pricing, etc.)

Development Support:
- Environment variables template
- Database seed script with realistic test data
- TypeScript configuration optimized for Nest.js
- Package.json with all required dependencies

Resolves database requirements from issues §78-81 establishing
the complete data layer foundation for the AI Bulk Image Renamer SaaS.

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

packages/api/src/database/database.module.ts

@@ -0,0 +1,27 @@
+import { Module, Global } from '@nestjs/common';
+import { ConfigModule } from '@nestjs/config';
+import { PrismaService } from './prisma.service';
+import { UserRepository } from './repositories/user.repository';
+import { BatchRepository } from './repositories/batch.repository';
+import { ImageRepository } from './repositories/image.repository';
+import { PaymentRepository } from './repositories/payment.repository';
+
+@Global()
+@Module({
+  imports: [ConfigModule],
+  providers: [
+    PrismaService,
+    UserRepository,
+    BatchRepository,
+    ImageRepository,
+    PaymentRepository,
+  ],
+  exports: [
+    PrismaService,
+    UserRepository,
+    BatchRepository,
+    ImageRepository,
+    PaymentRepository,
+  ],
+})
+export class DatabaseModule {}