feat(engine): replace docked touch bar with floating glass tab bar

Touch layout only (desktop bar unchanged): a floating glass pill
(Undo / Draw / Hint / Pause) plus a detached circular Menu button,
margin above the bottom edge on top of the safe-area inset. Draw is
the persistently expanded accent pill (icon + label); other buttons
are icon-only and slide their label out while pressed, snapping under
reduce-motion. Buttons keep the existing marker components so click
handlers, tooltips, focus ring, and chrome toggle work unchanged.
Icons: None degrades to text-fallback labels (MinimalPlugins tests /
SVG regression), keeping the bar fully usable.

Toast stack clearance now derives from TAB_BAR_CLEARANCE_PX; the
legacy touch bar spawn path and primary-button metrics are removed.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

solitaire_engine/src/animation_plugin.rs

@@ -179,10 +179,13 @@ pub struct ToastStackRoot;
 pub struct ToastNode;
 
 /// Logical-pixel gap between the screen bottom and the toast stack,
-/// before safe-area insets. Clears the Phase F bottom action bar on
-/// touch (compact 44px buttons + primary 64px trio + bar padding);
-/// desktop's shorter bar needs less.
-const TOAST_STACK_BASE_BOTTOM_PX: f32 = if USE_TOUCH_UI_LAYOUT { 112.0 } else { 72.0 };
+/// before safe-area insets. Clears the floating glass tab bar on touch
+/// (its margin + height + breathing room); desktop's docked bar needs less.
+const TOAST_STACK_BASE_BOTTOM_PX: f32 = if USE_TOUCH_UI_LAYOUT {
+    crate::hud_plugin::tab_bar::TAB_BAR_CLEARANCE_PX
+} else {
+    72.0
+};
 
 /// Spawns the persistent [`ToastStackRoot`] container at startup.
 fn spawn_toast_stack_root(mut commands: Commands) {