fix(common): 修复@genex/common包TypeScript编译错误

- current-user.decorator: 移除显式返回类型以兼容undefined字段访问
- http-exception.filter: 为message变量提供默认值避免TS2454

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

backend/packages/common/src/decorators/current-user.decorator.ts

@@ -6,7 +6,7 @@ import { JwtPayload } from '../interfaces/jwt-payload.interface';
  * Usage: @CurrentUser() user: JwtPayload
  */
 export const CurrentUser = createParamDecorator(
-  (data: keyof JwtPayload | undefined, ctx: ExecutionContext): JwtPayload => {
+  (data: keyof JwtPayload | undefined, ctx: ExecutionContext) => {
     const request = ctx.switchToHttp().getRequest();
     const user = request.user as JwtPayload;
     return data ? user?.[data] : user;

backend/packages/common/src/filters/http-exception.filter.ts

@@ -22,7 +22,7 @@ export class AllExceptionsFilter implements ExceptionFilter {
     const request = ctx.getRequest<Request>();
 
     let status: number;
-    let message: string;
+    let message: string = 'Unknown error';
     let details: any;
 
     if (exception instanceof HttpException) {