feat(engine): reduce-transparency + high-contrast support for glass chrome

New Settings::reduce_transparency_mode (serde-default, Accessibility
toggle row) swaps every GlassSurface's gradients for a flat opaque
BG_ELEVATED fill; high-contrast mode now also boosts the glass fill
opacity and rim luminance to BORDER_SUBTLE_HC levels. Both applied by
settings_plugin::update_glass_surfaces, which retargets the gradients
in place on toggle or on newly spawned glass.

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

solitaire_engine/src/settings_plugin/mod.rs

@@ -135,6 +135,10 @@ struct HighContrastText;
 #[derive(Component, Debug)]
 struct ReduceMotionText;
 
+/// Marks the `Text` node showing the current reduce-transparency state.
+#[derive(Component, Debug)]
+struct ReduceTransparencyText;
+
 /// Marks the `Text` node showing the current touch input mode state.
 #[derive(Component, Debug)]
 struct TouchInputModeText;
@@ -277,6 +281,10 @@ enum SettingsButton {
     /// non-essential motion (card-slide animations become instant
     /// snaps) per `design-system.md` §Accessibility (#3).
     ToggleReduceMotion,
+    /// Toggle the [`Settings::reduce_transparency_mode`] flag — swaps
+    /// translucent glass chrome (the floating touch tab bar) for opaque
+    /// fills so table content never bleeds through UI text.
+    ToggleReduceTransparency,
     /// Toggle [`Settings::touch_input_mode`] between `OneTap`
     /// (auto-move on tap, default) and `TapToSelect` (first tap selects
     /// a card/stack, second tap on a target pile moves it).
@@ -361,8 +369,9 @@ impl SettingsButton {
             // run before continuing to the picker rows.
             SettingsButton::ToggleHighContrast => 61,
             SettingsButton::ToggleReduceMotion => 62,
-            SettingsButton::ToggleTouchInputMode => 63,
-            SettingsButton::CycleUiScale => 64,
+            SettingsButton::ToggleReduceTransparency => 63,
+            SettingsButton::ToggleTouchInputMode => 64,
+            SettingsButton::CycleUiScale => 65,
             // Picker rows — every swatch in a row shares the row's
             // priority so entity-index tiebreaking yields left → right.
             SettingsButton::SelectCardBack(_) => 70,
@@ -514,6 +523,16 @@ impl Plugin for SettingsPlugin {
                     update_smart_default_size_text,
                 ),
             );
+            app.add_systems(
+                Update,
+                (
+                    update_reduce_transparency_text,
+                    // Guards internally on settings-change / newly added
+                    // glass — `Added<GlassSurface>` can't be expressed as
+                    // a resource run condition.
+                    update_glass_surfaces,
+                ),
+            );
             app.add_systems(
                 Update,
                 (