Show a muted "in sync" for submodules without issues

An empty status cell could be read as missing data. The muted word
confirms the check ran without drawing attention. The word is defined
once in the theme and shared with the detail pane.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

internal/tui/tree/tree.go

@@ -398,7 +398,8 @@ func (m Model) nodeLine(r row, nameColW, refW int) string {
 	name := ansi.Truncate(s.Name, max(nameW-len(count), 1), "…")
 	nameCell := seg(textColor, name) + seg(t.Muted, count) + pad(nameW-lipgloss.Width(name+count))
 
-	// status: the most severe issue as a word, "+n" for further issues
+	// status: the most severe issue as a word, "+n" for further issues;
+	// a muted "in sync" without issues, so an empty cell never looks broken
 	var status string
 	switch {
 	case s.Err != nil:
@@ -410,6 +411,8 @@ func (m Model) nodeLine(r row, nameColW, refW int) string {
 		if len(issues) > 1 {
 			status += seg(t.Muted, fmt.Sprintf(" +%d", len(issues)-1))
 		}
+	default:
+		status = seg(t.Muted, theme.InSync)
 	}
 	if k, worst := s.HiddenIssues(); collapsed && k > 0 {
 		if status != "" {