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/assets/hud_icon_svg.rs

@@ -82,10 +82,7 @@ impl HudIcon {
     /// Rasterise this icon into a Bevy [`Image`] at
     /// [`HUD_ICON_TEXTURE_PX`] square.
     pub fn rasterize(self) -> Result<Image, SvgLoaderError> {
-        rasterize_svg(
-            self.svg().as_bytes(),
-            UVec2::splat(HUD_ICON_TEXTURE_PX),
-        )
+        rasterize_svg(self.svg().as_bytes(), UVec2::splat(HUD_ICON_TEXTURE_PX))
     }
 }