fix: SFTP stacked mode — render only active pane + indicator bar

Stacked mode (<50 cols) now shows only the active pane (Local/Remote)
with a visual indicator bar. Tab switches between panes. Side-by-side
mode (>=50 cols) unchanged.

pkg/tui/sftp_browser_tab.go

@@ -543,14 +543,33 @@ func (t *SFTPBrowserTab) View() string {
 	// Responsive pane layout: stack vertically on narrow terminals
 	// Each pane renders at maxW+2 total (maxW content + 2 border chars)
 	var leftView, rightView string
+	var indicator string
 	if t.width < 50 {
-		// Stack vertically — each pane gets full width minus border
+		// Only show active pane in stacked mode — Tab switches between them
 		paneW := t.width - 2
 		if paneW < 20 {
 			paneW = 20
 		}
-		leftView = t.renderPane(&t.left, paneLocal, paneW)
-		rightView = t.renderPane(&t.right, paneRemote, paneW)
+		// Pane indicator: [Local]  Remote  or  Local  [Remote]
+		var indicatorParts []string
+		for _, name := range []string{"Local", "Remote"} {
+			pt := paneLocal
+			if name == "Remote" {
+				pt = paneRemote
+			}
+			if t.active == pt {
+				indicatorParts = append(indicatorParts, StatusBarStyle.Render(" "+name+" "))
+			} else {
+				indicatorParts = append(indicatorParts, SubtitleStyle.Render(" "+name+" "))
+			}
+		}
+		indicator = lipgloss.JoinHorizontal(lipgloss.Top, indicatorParts[0], SubtitleStyle.Render(" "), indicatorParts[1])
+
+		if t.active == paneLocal {
+			leftView = t.renderPane(&t.left, paneLocal, paneW)
+		} else {
+			leftView = t.renderPane(&t.right, paneRemote, paneW)
+		}
 	} else {
 		// Side by side — reserve 2 chars border per pane
 		halfW := t.width/2 - 2
@@ -568,7 +587,9 @@ func (t *SFTPBrowserTab) View() string {
 	b.WriteString("\n")
 
 	if t.width < 50 {
-		b.WriteString(lipgloss.JoinVertical(lipgloss.Left, leftView, rightView))
+		b.WriteString(lipgloss.PlaceHorizontal(t.width, lipgloss.Center, indicator))
+		b.WriteString("\n")
+		b.WriteString(leftView)
 	} else {
 		b.WriteString(lipgloss.JoinHorizontal(lipgloss.Top, leftView, rightView))
 	}