fix(trading-service): 修复 Multer 类型缺失导致构建失败

使用内联类型替代 Express.Multer.File，避免 @types/multer 依赖

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

backend/services/trading-service/src/api/controllers/c2c.controller.ts

@@ -280,7 +280,7 @@ export class C2cController {
   @ApiResponse({ status: 200, description: '上传成功' })
   async uploadPaymentProof(
     @Param('orderNo') orderNo: string,
-    @UploadedFile() file: Express.Multer.File,
+    @UploadedFile() file: { originalname: string; buffer: Buffer; mimetype: string; size: number },
     @Req() req: any,
   ): Promise<C2cOrderResponseDto> {
     const accountSequence = req.user?.accountSequence;