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/.env.example

@@ -0,0 +1,51 @@
+# Database
+DATABASE_URL="postgresql://username:password@localhost:5432/seo_image_renamer?schema=public"
+
+# Application
+NODE_ENV="development"
+PORT=3001
+API_PREFIX="api/v1"
+
+# JWT Configuration
+JWT_SECRET="your-super-secret-jwt-key-here"
+JWT_EXPIRES_IN="7d"
+
+# Google OAuth
+GOOGLE_CLIENT_ID="your-google-client-id"
+GOOGLE_CLIENT_SECRET="your-google-client-secret"
+GOOGLE_REDIRECT_URI="http://localhost:3001/api/v1/auth/google/callback"
+
+# Stripe Configuration
+STRIPE_SECRET_KEY="sk_test_your_stripe_secret_key"
+STRIPE_PUBLISHABLE_KEY="pk_test_your_stripe_publishable_key"
+STRIPE_WEBHOOK_SECRET="whsec_your_stripe_webhook_secret"
+
+# AWS S3 Configuration
+AWS_ACCESS_KEY_ID="your-aws-access-key"
+AWS_SECRET_ACCESS_KEY="your-aws-secret-key"
+AWS_REGION="us-east-1"
+AWS_S3_BUCKET="seo-image-renamer-uploads"
+
+# OpenAI Configuration
+OPENAI_API_KEY="sk-your-openai-api-key"
+OPENAI_MODEL="gpt-4-vision-preview"
+
+# Frontend URL (for CORS)
+FRONTEND_URL="http://localhost:3000"
+
+# Redis (for caching and queues)
+REDIS_URL="redis://localhost:6379"
+
+# Email Configuration (optional)
+SMTP_HOST="smtp.gmail.com"
+SMTP_PORT=587
+SMTP_USER="your-email@gmail.com"
+SMTP_PASS="your-email-password"
+FROM_EMAIL="noreply@seo-image-renamer.com"
+
+# Monitoring (optional)
+SENTRY_DSN="https://your-sentry-dsn"
+
+# Rate Limiting
+RATE_LIMIT_TTL=60
+RATE_LIMIT_LIMIT=10