feat: Full petmaster CRM with NestJS API and React frontend

- Client management (CRUD with JSONB custom fields)
- Pet profiles
- Service catalog with per-client pricing
- Booking calendar with recurring appointments
- Invoicing with Stripe integration
- Real-time messaging (WebSocket)
- Self-booking portal
- Staff assignment
- Docker multi-stage builds
- Prisma schema + seed

api/src/clients/dto/client.dto.ts

@@ -0,0 +1,74 @@
+import { IsEmail, IsOptional, IsString, IsBoolean } from 'class-validator';
+
+export class CreateClientDto {
+  @IsString()
+  firstName: string;
+
+  @IsString()
+  lastName: string;
+
+  @IsEmail()
+  email: string;
+
+  @IsString()
+  @IsOptional()
+  phone?: string;
+
+  @IsString()
+  @IsOptional()
+  address?: string;
+
+  @IsString()
+  @IsOptional()
+  notes?: string;
+
+  @IsOptional()
+  customFields?: Record<string, any>;
+}
+
+export class UpdateClientDto {
+  @IsString()
+  @IsOptional()
+  firstName?: string;
+
+  @IsString()
+  @IsOptional()
+  lastName?: string;
+
+  @IsEmail()
+  @IsOptional()
+  email?: string;
+
+  @IsString()
+  @IsOptional()
+  phone?: string;
+
+  @IsString()
+  @IsOptional()
+  address?: string;
+
+  @IsString()
+  @IsOptional()
+  notes?: string;
+
+  @IsOptional()
+  customFields?: Record<string, any>;
+}
+
+export class ListClientsQueryDto {
+  @IsOptional()
+  @IsString()
+  search?: string;
+
+  @IsOptional()
+  @IsBoolean()
+  isActive?: boolean;
+
+  @IsOptional()
+  @IsString()
+  page?: string;
+
+  @IsOptional()
+  @IsString()
+  limit?: string;
+}