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/responsive.go

@@ -0,0 +1,108 @@
+package tui
+
+import (
+	"strings"
+
+	"github.com/charmbracelet/lipgloss"
+)
+
+// Responsive breakpoints
+const (
+	widthCompact = 60  // mobile / Termux
+	widthMedium  = 100 // tablet
+)
+
+// boxOverhead is the horizontal chars consumed by BorderStyle (border 2 + padding 4)
+const boxOverhead = 6
+
+// wrapFooter wraps a footer string into multiple lines that fit availW.
+// Words are split on double-space separators ("  ") and grouped greedily.
+// Returns the wrapped string with "\n" line breaks.
+func wrapFooter(text string, availW int) string {
+	if availW < 1 {
+		availW = 1
+	}
+	if lipgloss.Width(text) <= availW {
+		return text
+	}
+
+	words := strings.Split(text, "  ")
+	var lines []string
+	var current strings.Builder
+
+	for _, word := range words {
+		word = strings.TrimSpace(word)
+		if word == "" {
+			continue
+		}
+		if current.Len() == 0 {
+			current.WriteString(word)
+		} else if current.Len()+2+lipgloss.Width(word) <= availW {
+			current.WriteString("  ")
+			current.WriteString(word)
+		} else {
+			lines = append(lines, current.String())
+			current.Reset()
+			current.WriteString(word)
+		}
+	}
+	if current.Len() > 0 {
+		lines = append(lines, current.String())
+	}
+
+	return strings.Join(lines, "\n")
+}
+
+// adaptiveSidePad returns horizontal padding based on terminal width.
+// wide: 6, medium: 3, compact: 1
+func adaptiveSidePad(termWidth int) int {
+	switch {
+	case termWidth < widthCompact:
+		return 1
+	case termWidth < widthMedium:
+		return 3
+	default:
+		return 6
+	}
+}
+
+// clampWidth clamps a target box width to fit within the terminal.
+// Reserves boxOverhead for border+padding. Enforces a minimum of 20.
+func clampWidth(target, termWidth int) int {
+	maxW := termWidth - boxOverhead
+	if maxW < 20 {
+		maxW = 20
+	}
+	if target > maxW {
+		return maxW
+	}
+	if target < 20 {
+		return 20
+	}
+	return target
+}
+
+// truncateStr truncates a string to maxLen with an ellipsis character.
+func truncateStr(s string, maxLen int) string {
+	if maxLen < 1 {
+		return ""
+	}
+	if lipgloss.Width(s) <= maxLen {
+		return s
+	}
+	if maxLen <= 1 {
+		return "…"
+	}
+	runes := []rune(s)
+	var result []rune
+	resultW := 0
+	for _, r := range runes {
+		rw := lipgloss.Width(string(r))
+		if resultW+rw > maxLen-1 {
+			break
+		}
+		result = append(result, r)
+		resultW += rw
+	}
+	return string(result) + "…"
+}