feat: add notification triggers, comment roles, mention list, and static file serving

- Notify users on ticket assignment and remittance confirm/reject
- Add collector role to comment endpoints
- Add /users/mention-list endpoint for @mention support
- Serve uploaded files via express.static

src/comment/comment.controller.ts

@@ -24,7 +24,7 @@ export class CommentController {
   constructor(private readonly commentService: CommentService) {}
 
   @Get()
-  @Roles('technician')
+  @Roles('technician', 'collector')
   async findAll(
     @CurrentUser() user: CurrentUserPayload,
     @Param('ticketId') ticketId: string,
@@ -33,7 +33,7 @@ export class CommentController {
   }
 
   @Post()
-  @Roles('technician')
+  @Roles('technician', 'collector')
   @UseInterceptors(FileFieldsInterceptor([{ name: 'files', maxCount: 3 }], multerOptions))
   async create(
     @CurrentUser() user: CurrentUserPayload,