feat(handler): update GetFile and ListFiles handlers for new FileResponse fields

- GetFile uses new GetFileResponse instead of manual FileResponse construction

- ListFiles handler parses optional user_id query parameter

- Wire FolderStore into FileService in app.go, testenv, and file_test

Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-openagent)

Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>

internal/testutil/testenv/env.go

@@ -180,7 +180,7 @@ func NewTestEnv(t interface {
 	taskSvc := service.NewTaskService(taskStore, appStore, fileStore, blobStore, stagingSvc, jobSvc, workDir, logger)
 	appSvc := service.NewApplicationService(appStore, jobSvc, workDir, logger, taskSvc)
 	uploadSvc := service.NewUploadService(mockMinIO, blobStore, fileStore, uploadStore, minioCfg, db, logger)
-	fileSvc := service.NewFileService(mockMinIO, blobStore, fileStore, minioCfg.Bucket, db, logger)
+	fileSvc := service.NewFileService(mockMinIO, blobStore, fileStore, folderStore, minioCfg.Bucket, db, logger)
 
 	// 9. All 7 Handler instances
 	jobH := handler.NewJobHandler(jobSvc, logger)