fix stale link detection when base files dir missing

internal/core/ops.go

@@ -154,6 +154,13 @@ func FindStaleLinksMulti(filesDirs []string, targetRoot string) ([]string, error
 
 	// First pass: walk source directories to find files that exist
 	for _, filesDir := range filesDirs {
+		if _, err := os.Stat(filesDir); err != nil {
+			if errors.Is(err, os.ErrNotExist) {
+				continue
+			}
+			return nil, err
+		}
+
 		filesAbs, err := filepath.Abs(filesDir)
 		if err != nil {
 			return nil, err