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/users/users.entity.ts

@@ -0,0 +1,203 @@
+import { 
+  IsEmail, 
+  IsString, 
+  IsEnum, 
+  IsInt, 
+  IsBoolean, 
+  IsOptional, 
+  IsUUID, 
+  Min,
+  IsDate 
+} from 'class-validator';
+import { ApiProperty, ApiPropertyOptional } from '@nestjs/swagger';
+import { Plan } from '@prisma/client';
+
+export class CreateUserDto {
+  @ApiPropertyOptional({ 
+    description: 'Google OAuth UID for OAuth integration',
+    example: 'google_123456789'
+  })
+  @IsOptional()
+  @IsString()
+  googleUid?: string;
+
+  @ApiProperty({ 
+    description: 'User email address',
+    example: 'user@example.com'
+  })
+  @IsEmail()
+  email: string;
+
+  @ApiProperty({ 
+    description: 'Hashed version of email for privacy',
+    example: 'a665a45920422f9d417e4867efdc4fb8a04a1f3fff1fa07e998e86f7f7a27ae3'
+  })
+  @IsString()
+  emailHash: string;
+
+  @ApiPropertyOptional({ 
+    description: 'User subscription plan',
+    enum: Plan,
+    default: Plan.BASIC
+  })
+  @IsOptional()
+  @IsEnum(Plan)
+  plan?: Plan;
+
+  @ApiPropertyOptional({ 
+    description: 'Remaining quota for current period',
+    example: 50,
+    minimum: 0
+  })
+  @IsOptional()
+  @IsInt()
+  @Min(0)
+  quotaRemaining?: number;
+}
+
+export class UpdateUserDto {
+  @ApiPropertyOptional({ 
+    description: 'User subscription plan',
+    enum: Plan
+  })
+  @IsOptional()
+  @IsEnum(Plan)
+  plan?: Plan;
+
+  @ApiPropertyOptional({ 
+    description: 'Remaining quota for current period',
+    minimum: 0
+  })
+  @IsOptional()
+  @IsInt()
+  @Min(0)
+  quotaRemaining?: number;
+
+  @ApiPropertyOptional({ 
+    description: 'Whether the user account is active'
+  })
+  @IsOptional()
+  @IsBoolean()
+  isActive?: boolean;
+}
+
+export class UserResponseDto {
+  @ApiProperty({ 
+    description: 'Unique user identifier',
+    example: '550e8400-e29b-41d4-a716-446655440000'
+  })
+  @IsUUID()
+  id: string;
+
+  @ApiPropertyOptional({ 
+    description: 'Google OAuth UID',
+    example: 'google_123456789'
+  })
+  @IsOptional()
+  @IsString()
+  googleUid?: string;
+
+  @ApiProperty({ 
+    description: 'User email address',
+    example: 'user@example.com'
+  })
+  @IsEmail()
+  email: string;
+
+  @ApiProperty({ 
+    description: 'User subscription plan',
+    enum: Plan
+  })
+  @IsEnum(Plan)
+  plan: Plan;
+
+  @ApiProperty({ 
+    description: 'Remaining quota for current period',
+    example: 50
+  })
+  @IsInt()
+  @Min(0)
+  quotaRemaining: number;
+
+  @ApiProperty({ 
+    description: 'Date when quota resets'
+  })
+  @IsDate()
+  quotaResetDate: Date;
+
+  @ApiProperty({ 
+    description: 'Whether the user account is active'
+  })
+  @IsBoolean()
+  isActive: boolean;
+
+  @ApiProperty({ 
+    description: 'User creation timestamp'
+  })
+  @IsDate()
+  createdAt: Date;
+
+  @ApiProperty({ 
+    description: 'User last update timestamp'
+  })
+  @IsDate()
+  updatedAt: Date;
+}
+
+export class UserStatsDto {
+  @ApiProperty({ 
+    description: 'Total number of batches processed'
+  })
+  @IsInt()
+  @Min(0)
+  totalBatches: number;
+
+  @ApiProperty({ 
+    description: 'Total number of images processed'
+  })
+  @IsInt()
+  @Min(0)
+  totalImages: number;
+
+  @ApiProperty({ 
+    description: 'Current quota usage this period'
+  })
+  @IsInt()
+  @Min(0)
+  quotaUsed: number;
+
+  @ApiProperty({ 
+    description: 'Total quota for current plan'
+  })
+  @IsInt()
+  @Min(0)
+  totalQuota: number;
+
+  @ApiProperty({ 
+    description: 'Percentage of quota used'
+  })
+  @IsInt()
+  @Min(0)
+  quotaUsagePercentage: number;
+}
+
+// Helper function to get quota limits by plan
+export function getQuotaLimitForPlan(plan: Plan): number {
+  switch (plan) {
+    case Plan.BASIC:
+      return 50;
+    case Plan.PRO:
+      return 500;
+    case Plan.MAX:
+      return 1000;
+    default:
+      return 50;
+  }
+}
+
+// Helper function to calculate quota reset date (monthly)
+export function calculateQuotaResetDate(): Date {
+  const now = new Date();
+  const nextMonth = new Date(now.getFullYear(), now.getMonth() + 1, 1);
+  return nextMonth;
+}