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/hud_plugin/updates.rs

@@ -573,20 +573,6 @@ pub(super) fn action_button_metrics() -> (UiRect, Val, Val) {
     }
 }
 
-/// Metrics for the touch bar's enlarged Undo / Draw / Hint trio (Phase F).
-/// 96×64 px targets — comfortably past the 44 px accessibility floor and
-/// big enough to hit one-handed without looking. Only the touch layout
-/// spawns primary buttons, so no desktop branch is needed; the desktop
-/// values exist purely so host-side tests can exercise the touch spawn
-/// path with sensible numbers.
-pub(super) fn primary_action_button_metrics() -> (UiRect, Val, Val) {
-    (
-        UiRect::axes(Val::Px(10.0), Val::Px(8.0)),
-        Val::Px(96.0),
-        Val::Px(64.0),
-    )
-}
-
 pub(super) fn spawn_action_button_label(
     parent: &mut ChildSpawnerCommands,
     label: &str,