feat(engine): UI scale setting — 90/100/115/130% (Phase K)

Settings -> Accessibility gains a UI Scale row cycling four steps,
applied live through bevy::ui::UiScale: every menu, modal, and HUD
element scales while the table itself stays window-fit via
compute_layout. New Settings::ui_scale (serde default 1.0, sanitized
clamp to [0.9, 1.3]).

Safe-area anchors and modal scrim padding pre-divide physical insets
by the UI scale so post-multiplication lands exactly on the system
bars — without this, 90% would sink the bottom action bar into the
Android gesture zone. The anchor systems also re-run on UiScale
changes, not just inset changes.

Deferred from Phase K (noted in the doc): seeding the setting from the
Android system font scale on first run (needs JNI), and the 44px
touch-target audit (on-device).

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

solitaire_engine/src/settings_plugin/ui.rs

@@ -326,6 +326,15 @@ fn spawn_accessibility_tab(
         "One-tap: tap a card to auto-move it. Tap to select: first tap selects a card, second tap on a pile moves it.",
         font_res,
     );
+    toggle_row(
+        body,
+        "UI Scale",
+        UiScaleText,
+        ui_scale_label(settings.ui_scale),
+        SettingsButton::CycleUiScale,
+        "Scales all menus, buttons, and HUD text. The table itself always fits the screen.",
+        font_res,
+    );
     tooltip_delay_row(body, settings.tooltip_delay_secs, font_res);
 }