refactor: delegate -l output to findmnt

The custom one-alias-per-line output was useless — no mountpoint, no
source, no options. Reinventing a table format when findmnt from
util-linux already produces a familiar fuse.sshfs view was the wrong
call. -l now shells out to findmnt -t fuse.sshfs.

main.go

@@ -281,26 +281,22 @@ func is_mounted_at(path string) (bool, error) {
 }
 
 func list_mounts(out io.Writer) error {
-	base, err := mount_base(false)
-	if err != nil {
-		if errors.Is(err, fs.ErrNotExist) {
-			return nil
-		}
-		return err
+	cmd := exec.Command("findmnt", "-t", "fuse.sshfs")
+	cmd.Stdout = out
+	cmd.Stderr = os.Stderr
+	err := cmd.Run()
+	if err == nil {
+		return nil
 	}
-	mounts, err := mountinfo.GetMounts(mountinfo.PrefixFilter(base))
-	if err != nil {
-		return fmt.Errorf("read mountinfo: %w", err)
+	// findmnt exits 1 when no matching mount exists — not an error here.
+	var ee *exec.ExitError
+	if errors.As(err, &ee) && ee.ExitCode() == 1 {
+		return nil
 	}
-	prefix := base + string(os.PathSeparator)
-	for _, m := range mounts {
-		rel := strings.TrimPrefix(m.Mountpoint, prefix)
-		if rel == "" || strings.Contains(rel, string(os.PathSeparator)) {
-			continue
-		}
-		fmt.Fprintln(out, rel)
+	if errors.Is(err, exec.ErrNotFound) {
+		return fmt.Errorf("findmnt not found (install util-linux)")
 	}
-	return nil
+	return fmt.Errorf("findmnt: %w", err)
 }
 
 func run_fusermount(flag, mount string) error {