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/fx.rs

@@ -109,12 +109,19 @@ pub(super) fn apply_action_fade(
 /// Visual feedback for every action button — paints idle / hover / pressed
 /// states by mutating `BackgroundColor` whenever the interaction state
 /// changes. One query covers all action buttons via the shared
-/// `ActionButton` marker.
+/// `ActionButton` marker. Glass tab-bar buttons are excluded: they carry
+/// their own per-button colour triple and are painted by
+/// `paint_glass_tab_buttons` instead (this system's opaque `ACTION_BTN_*`
+/// fills would destroy the translucent glass look).
 #[allow(clippy::type_complexity)]
 pub(super) fn paint_action_buttons(
     mut buttons: Query<
         (&Interaction, &mut BackgroundColor),
-        (With<ActionButton>, Changed<Interaction>),
+        (
+            With<ActionButton>,
+            Without<GlassTabButton>,
+            Changed<Interaction>,
+        ),
     >,
 ) {
     for (interaction, mut bg) in &mut buttons {