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/ui.rs

@@ -317,6 +317,15 @@ fn spawn_accessibility_tab(
         "Skips card-slide animations and other non-essential motion. Cards snap instantly to their target.",
         font_res,
     );
+    toggle_row(
+        body,
+        "Reduce Transparency",
+        ReduceTransparencyText,
+        on_off_label(settings.reduce_transparency_mode),
+        SettingsButton::ToggleReduceTransparency,
+        "Replaces the see-through glass toolbar with a solid panel so cards behind it never reduce readability.",
+        font_res,
+    );
     toggle_row(
         body,
         "Touch Input Mode",