fix(comment): Create proper DTO class for comment creation

- Create CreateCommentDto class with proper validation decorators
- Update comment controller to use the DTO for request body
- This resolves the global ValidationPipe rejection due to forbidNonWhitelisted
- Set MaxLength to 50000 to match manual validation logic

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

src/comment/dto/create-comment.dto.ts

@@ -1,7 +1,19 @@
-import { IsString, MinLength } from 'class-validator';
+import {
+  IsString,
+  IsOptional,
+  IsArray,
+  MinLength,
+  MaxLength,
+} from 'class-validator';
 
 export class CreateCommentDto {
   @IsString()
   @MinLength(1)
-  content!: string;
+  @MaxLength(50000)
+  content: string;
+
+  @IsOptional()
+  @IsArray()
+  @IsString({ each: true })
+  files?: string[];
 }