feat: Implement real-time messaging module with REST API endpoints and WebSocket gateway.

src/messages/dto/create-message.dto.ts

@@ -0,0 +1,35 @@
+import { IsString, IsNotEmpty, IsOptional, IsEnum, MaxLength } from 'class-validator';
+import { ApiProperty, ApiPropertyOptional } from '@nestjs/swagger';
+import { MessageType } from '@prisma/client';
+
+export class CreateMessageDto {
+  @ApiProperty({ description: 'Message content', maxLength: 5000 })
+  @IsString()
+  @IsNotEmpty()
+  @MaxLength(5000)
+  content: string;
+
+  @ApiPropertyOptional({ description: 'Message type', enum: MessageType, default: MessageType.TEXT })
+  @IsOptional()
+  @IsEnum(MessageType)
+  messageType?: MessageType = MessageType.TEXT;
+
+  @ApiPropertyOptional({ description: 'File URL for file/image messages' })
+  @IsOptional()
+  @IsString()
+  fileUrl?: string;
+
+  @ApiPropertyOptional({ description: 'Original file name' })
+  @IsOptional()
+  @IsString()
+  fileName?: string;
+
+  @ApiPropertyOptional({ description: 'File size in bytes' })
+  @IsOptional()
+  fileSize?: number;
+
+  @ApiPropertyOptional({ description: 'MIME type of the file' })
+  @IsOptional()
+  @IsString()
+  mimeType?: string;
+}