fix(restore): propagate src.Close() error in copyFileIntoZip

If io.Copy succeeded but src.Close() failed, the close error was
silently discarded. Preserve the intent of not using defer (to avoid
accumulating open handles across Walk iterations) while returning the
close error when no copy error occurred.

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

Author: greynewell

cmd/restore.go

@@ -245,7 +245,9 @@ func copyFileIntoZip(path string, w io.Writer) error {
 		return err
 	}
 	_, err = io.Copy(w, src)
-	src.Close()
+	if closeErr := src.Close(); err == nil {
+		err = closeErr
+	}
 	return err
 }