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/prisma/schema.prisma

@@ -0,0 +1,179 @@
+// This is your Prisma schema file,
+// learn more about it in the docs: https://pris.ly/d/prisma-schema
+
+generator client {
+  provider = "prisma-client-js"
+}
+
+datasource db {
+  provider = "postgresql"
+  url      = env("DATABASE_URL")
+}
+
+// Enum for user subscription plans
+enum Plan {
+  BASIC // 50 images per month
+  PRO   // 500 images per month
+  MAX   // 1000 images per month
+}
+
+// Enum for batch processing status
+enum BatchStatus {
+  PROCESSING
+  DONE
+  ERROR
+}
+
+// Enum for individual image processing status
+enum ImageStatus {
+  PENDING
+  PROCESSING
+  COMPLETED
+  FAILED
+}
+
+// Enum for payment status
+enum PaymentStatus {
+  PENDING
+  COMPLETED
+  FAILED
+  CANCELLED
+  REFUNDED
+}
+
+// Users table - OAuth ready with Google integration
+model User {
+  id              String   @id @default(uuid())
+  googleUid       String?  @unique @map("google_uid") // Google OAuth UID
+  emailHash       String   @unique @map("email_hash") // Hashed email for privacy
+  email           String   @unique // Actual email for communication
+  plan            Plan     @default(BASIC)
+  quotaRemaining  Int      @default(50) @map("quota_remaining") // Monthly quota
+  quotaResetDate  DateTime @default(now()) @map("quota_reset_date") // When quota resets
+  isActive        Boolean  @default(true) @map("is_active")
+  createdAt       DateTime @default(now()) @map("created_at")
+  updatedAt       DateTime @updatedAt @map("updated_at")
+
+  // Relations
+  batches  Batch[]
+  payments Payment[]
+  apiKeys  ApiKey[]
+
+  @@map("users")
+  @@index([emailHash])
+  @@index([googleUid])
+  @@index([plan])
+}
+
+// Batches table - Groups of images processed together
+model Batch {
+  id          String      @id @default(uuid())
+  userId      String      @map("user_id")
+  status      BatchStatus @default(PROCESSING)
+  totalImages Int         @default(0) @map("total_images")
+  processedImages Int     @default(0) @map("processed_images")
+  failedImages    Int     @default(0) @map("failed_images")
+  metadata    Json?       // Additional batch metadata (e.g., processing settings)
+  createdAt   DateTime    @default(now()) @map("created_at")
+  updatedAt   DateTime    @updatedAt @map("updated_at")
+  completedAt DateTime?   @map("completed_at")
+
+  // Relations
+  user   User    @relation(fields: [userId], references: [id], onDelete: Cascade)
+  images Image[]
+
+  @@map("batches")
+  @@index([userId])
+  @@index([status])
+  @@index([createdAt])
+}
+
+// Images table - Individual images within batches
+model Image {
+  id            String      @id @default(uuid())
+  batchId       String      @map("batch_id")
+  originalName  String      @map("original_name")
+  proposedName  String?     @map("proposed_name") // AI-generated name
+  finalName     String?     @map("final_name") // User-approved final name
+  visionTags    Json?       @map("vision_tags") // AI vision analysis results
+  status        ImageStatus @default(PENDING)
+  fileSize      Int?        @map("file_size") // File size in bytes
+  dimensions    Json?       // Width/height as JSON object
+  mimeType      String?     @map("mime_type")
+  s3Key         String?     @map("s3_key") // S3 object key for storage
+  processingError String?   @map("processing_error") // Error message if processing failed
+  createdAt     DateTime    @default(now()) @map("created_at")
+  updatedAt     DateTime    @updatedAt @map("updated_at")
+  processedAt   DateTime?   @map("processed_at")
+
+  // Relations
+  batch Batch @relation(fields: [batchId], references: [id], onDelete: Cascade)
+
+  @@map("images")
+  @@index([batchId])
+  @@index([status])
+  @@index([originalName])
+  @@index([createdAt])
+}
+
+// Payments table - Stripe integration for subscription management
+model Payment {
+  id              String        @id @default(uuid())
+  userId          String        @map("user_id")
+  stripeSessionId String?       @unique @map("stripe_session_id") // Stripe Checkout Session ID
+  stripePaymentId String?       @unique @map("stripe_payment_id") // Stripe Payment Intent ID
+  plan            Plan          // The plan being purchased
+  amount          Int           // Amount in cents
+  currency        String        @default("usd")
+  status          PaymentStatus @default(PENDING)
+  metadata        Json?         // Additional payment metadata
+  createdAt       DateTime      @default(now()) @map("created_at")
+  updatedAt       DateTime      @updatedAt @map("updated_at")
+  paidAt          DateTime?     @map("paid_at")
+
+  // Relations
+  user User @relation(fields: [userId], references: [id], onDelete: Cascade)
+
+  @@map("payments")
+  @@index([userId])
+  @@index([status])
+  @@index([stripeSessionId])
+  @@index([createdAt])
+}
+
+// API Keys table - For potential API access
+model ApiKey {
+  id        String   @id @default(uuid())
+  userId    String   @map("user_id")
+  keyHash   String   @unique @map("key_hash") // Hashed API key
+  name      String   // User-friendly name for the key
+  isActive  Boolean  @default(true) @map("is_active")
+  lastUsed  DateTime? @map("last_used")
+  createdAt DateTime @default(now()) @map("created_at")
+  updatedAt DateTime @updatedAt @map("updated_at")
+  expiresAt DateTime? @map("expires_at")
+
+  // Relations
+  user  User           @relation(fields: [userId], references: [id], onDelete: Cascade)
+  usage ApiKeyUsage[]
+
+  @@map("api_keys")
+  @@index([userId])
+  @@index([keyHash])
+  @@index([isActive])
+}
+
+// API Key Usage tracking
+model ApiKeyUsage {
+  id        String   @id @default(uuid())
+  apiKeyId  String   @map("api_key_id")
+  endpoint  String   // Which API endpoint was called
+  createdAt DateTime @default(now()) @map("created_at")
+
+  // Relations
+  apiKey ApiKey @relation(fields: [apiKeyId], references: [id], onDelete: Cascade)
+
+  @@map("api_key_usage")
+  @@index([apiKeyId])
+  @@index([createdAt])
+}