ui: remove keypad background container and its border

Per user request: eliminate the enclosing dark panel (bg 234 + NormalBorder)
around the entire key grid. Only the individual key styling remains
(bordered mini-panels with per-type colors, Height(2), pressed flash inversion).

- The rawGrid is now centered directly under the display using
  Width(dispW).Align(Center).
- BASE button still appears nicely centered on its row thanks to the
  uniform row width padding we added earlier.
- Keys sit directly on the main card background.
- Updated docs/UI_DESIGN.md to match.

Much cleaner and closer to a pure 'tactile keys only' look.

docs/UI_DESIGN.md

@@ -24,7 +24,7 @@ This layout keeps the galculator spirit (base visible at a glance next to the bi
 ## Keypad Grid (Tactile Decoration)
 Sparse for MVP (no memory, no %, no bitwise, no scientific, no A-F yet).
 
-The keypad is now decorated to evoke a physical, tactile calculator:
+The keypad is decorated to evoke a physical, tactile calculator using only the keys themselves (no enclosing background panel or outer border around the grid):
 
 - Each key is a bordered mini-panel (NormalBorder color 238) with its own background and foreground.
 - Base key style: dark bg 236, light fg 250, subtle border — gives a "raised key" appearance.
@@ -33,11 +33,12 @@ The keypad is now decorated to evoke a physical, tactile calculator:
   - Operators (+ - * / =): accent color 63 for quick recognition.
   - Clears (C, AC): red-tinted bg 52 + fg 203 (warning/danger).
   - MOD: highlighted (214 orange).
-  - BASE: prominent border color 63 + bold (the special display function).
+  - BASE: prominent border color 63 + bold (stands out as the special display function).
-- Pressed state: the key inverts to the bright flashStyle (white fg on 63 bg, bold border) for ~140ms on every action. This provides immediate "tactile click" visual feedback (modeled directly on gostations volume/skip/stop flashes).
+- Pressed state: the key inverts to the bright flashStyle (white fg on 63 bg, bold) for ~140ms on every action. This provides immediate "tactile click" visual feedback (modeled directly on gostations volume/skip/stop flashes).
 - Keys use Height(2) for chunkier, more button-like presence.
-- Spacing ("  " gaps) between keys and a backing panel (bg 234 + its own border) give the whole keypad a "faceplate" or "keyboard tray" look, making the individual keys pop as separate physical buttons.
+- Spacing ("  " gaps) between keys.
-- The entire keypad backing is full-width (matching the display) and centered.
+
+The keys sit directly on the main card background (no faceplate container).
 
 Layout sketch (subject to refinement; 4-5 columns):
 

internal/ui/ui.go

@@ -256,9 +256,9 @@ func (a *App) View() string {
 	row3 := lipgloss.JoinHorizontal(lipgloss.Top, makeKey("1"), spacer, makeKey("2"), spacer, makeKey("3"), spacer, makeKey("-"), spacer, makeKey("AC"))
 	row4 := lipgloss.JoinHorizontal(lipgloss.Top, makeKey("0"), spacer, makeKey("."), spacer, makeKey("+/-"), spacer, makeKey("+"), spacer, makeKey("="))
 
-	// Make the BASE row the same width as the other rows so the vertical join
+	// Make the BASE row the same width as the other rows.
-	// produces a clean rectangle. This fixes the chopped bottom border on BASE
+	// This ensures the BASE button is nicely centered on its own row
-	// and makes the backing panel dimensions match the actual keypad content.
+	// when the whole grid is centered under the display.
 	fullRowWidth := lipgloss.Width(row1)
 	baseOnly := makeKey("BASE")
 	baseRow := lipgloss.NewStyle().
@@ -266,25 +266,17 @@ func (a *App) View() string {
 		Align(lipgloss.Center).
 		Render(baseOnly)
 
-	// Compact grid of keys — now every row has identical width.
+	// Compact grid of keys — every row has identical width so the BASE
+	// button sits nicely centered on its row.
 	rawGrid := lipgloss.JoinVertical(lipgloss.Left, row1, row2, row3, row4, baseRow)
 
-	// Keypad backing panel sized *tightly* to the (now rectangular) grid content.
+	// Center the key grid directly under the display.
-	// Then we center the whole panel under the display. This makes the black
+	// No enclosing container or background panel — just the individually
-	// background exactly match the keypad's bounding box instead of having
+	// styled keys (each with their own border + color).
-	// dangling empty space on the sides of the BASE row.
 	keypad := lipgloss.NewStyle().
-		Border(lipgloss.NormalBorder()).
-		BorderForeground(lipgloss.Color("238")).
-		Background(lipgloss.Color("234")).
-		Padding(1, 2).
-		Render(rawGrid)
-
-	// Center the compact keypad panel under the wide display row.
-	keypad = lipgloss.NewStyle().
 		Width(dispW).
 		Align(lipgloss.Center).
-		Render(keypad)
+		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")