feat(server): Added GCS Read permission error

[hexaforce]

Overview

Add permission-error handling for GCS file downloads.

What I've done

Investigate whether permission-related errors occur when saving files to GCS in visualizer and visualizer-internal-api.

	if err != nil {
		if errors.Is(err, storage.ErrObjectNotExist) {
+			if OK := f.exists(ctx, bucket, filename); OK {
+				return nil, errors.New("no read permission")
+			}
			return nil, rerror.ErrNotFound
		}
		log.Errorfc(ctx, "gcs: generation read err: %+v\n", err)
		return nil, rerror.ErrInternalByWithContext(ctx, err)
	}

What I haven't done

How I tested

Which point I want you to review particularly

Memo