ui: simplify hint and remap clear keys

- Hint now exactly: "Tab:BASE  m:MOD  BackSpace:C  Del:AC"
- Removed all operator keys, numbers, equals, q:quit etc. from the hint per request.
- Remapped:
  - backspace key -> ClearEntry (flashes the visual 'C' button)
  - delete/del key -> AllClear (flashes the visual 'AC' button)
- Removed the old 'c','C' and 'ac','ctrl+l' handlers to match the new keymap.
- Updated docs/UI_DESIGN.md example to the new minimal hint.

The visual 'C' and 'AC' buttons remain in the grid for reference; their functions are now on Backspace and Del.

docs/UI_DESIGN.md

@@ -62,7 +62,7 @@ This decoration keeps the UI lightweight while making the keypad feel far more "
   - `lipgloss.Place(width, height, lipgloss.Center, lipgloss.Center, card)`
   - No stretching to full terminal width (important lesson from gostations player polish).
 - Subtle inner borders on panels where depth helps.
-- Minimal non-wrapping hint row at bottom of window (lipgloss bar with key badges in 63 bg, like final gostations player): e.g. "Tab:BASE  q:quit  etc."
+- Minimal non-wrapping hint row at bottom of window (lipgloss bar with key badges in 63 bg, like final gostations player): e.g. "Tab:BASE  m:MOD  BackSpace:C  Del:AC"
 - Resize handling: card recenters; display and grid adapt gracefully (minimum sensible width enforced with a message if too narrow).
 - Consistent dark theme, green LCD accents, flash feedback.
 

internal/ui/ui.go

@@ -84,15 +84,12 @@ func (a *App) Update(msg tea.Msg) (tea.Model, tea.Cmd) {
 			// The "base" flash will highlight the base label in the display row.
 			return a, tick(140*time.Millisecond, "base")
 
-		case "c", "C":
+		case "backspace":
 			a.engine.ClearEntry()
 			a.flash = "clear"
 			a.pressedKey = "C"
 			return a, tick(140*time.Millisecond, "key")
 
-		case "backspace":
-			a.engine.Backspace()
-
 		case ".":
 			a.engine.EnterDecimalPoint()
 			a.pressedKey = "."
@@ -121,7 +118,7 @@ func (a *App) Update(msg tea.Msg) (tea.Model, tea.Cmd) {
 			a.pressedKey = msg.String()
 			return a, tick(140*time.Millisecond, "key")
 
-		case "ac", "ctrl+l": // All Clear
+		case "delete", "del": // All Clear
 			a.engine.AllClear()
 			a.flash = "clear"
 			a.pressedKey = "AC"
@@ -265,7 +262,7 @@ func (a *App) View() string {
 		Render(rawGrid)
 
 	// Hint (minimal, non-wrapping, like gostations final player)
-	hint := lipgloss.NewStyle().Faint(true).Render("Tab:BASE  0-9 . = + - * / m:MOD  c:C  ac:AC  q:quit")
+	hint := lipgloss.NewStyle().Faint(true).Render("Tab:BASE  m:MOD  BackSpace:C  Del:AC")
 	centeredHint := lipgloss.NewStyle().Width(dispW).Align(lipgloss.Center).Render(hint)
 
 	inner := lipgloss.JoinVertical(lipgloss.Left,