feat: responsive TUI layout — mobile/tablet/desktop support

- NEW responsive.go: wrapFooter, adaptiveSidePad, clampWidth, truncateStr
- Footer auto-wraps to multi-line on narrow terminals (full labels preserved)
- Box width clamped to terminal width across all tabs
- Host/key/snippet rows truncated with ellipsis; compact format <35 cols
- SFTP panes stack vertically when terminal < 50 cols
- Tab bar truncates names on overflow
- Form contentW minimum lowered 50->30 for mobile
- Fixed: key_list_tab & snippet_list_tab dropped last data row (off-by-one bug)

pkg/tui/host_form_tab.go

@@ -293,8 +293,8 @@ func (t *HostFormTab) submit() (Tab, tea.Cmd) {
 
 func (t *HostFormTab) View() string {
 	contentW := t.width - 12
-	if contentW < 50 {
-		contentW = 50
+	if contentW < 30 {
+		contentW = 30
 	}
 	if contentW > 70 {
 		contentW = 70
@@ -358,8 +358,12 @@ func (t *HostFormTab) View() string {
 	}
 
 	inner.WriteString("\n")
-	inner.WriteString(lipgloss.PlaceHorizontal(contentW, lipgloss.Center,
-		SubtitleStyle.Render("Ctrl+Tab:switch  Ctrl+Q:close  Tab:next  Shift+Tab:prev  ↑↓:nav  Enter:next  Ctrl+S:save  Esc:cancel")))
+	footerText := "Ctrl+Tab:switch  Ctrl+Q:close  Tab:next  Shift+Tab:prev  ↑↓:nav  Enter:next  Ctrl+S:save  Esc:cancel"
+	footerWrapped := wrapFooter(footerText, contentW)
+	for _, line := range strings.Split(footerWrapped, "\n") {
+		inner.WriteString(lipgloss.PlaceHorizontal(contentW, lipgloss.Center, SubtitleStyle.Render(line)))
+		inner.WriteString("\n")
+	}
 
 	box := BorderStyle.Render(inner.String())
 	var b strings.Builder