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/input.rs

@@ -363,6 +363,14 @@ pub(super) fn handle_settings_buttons(
                 changed.write(SettingsChangedEvent(settings.0.clone()));
                 // Text refreshed by `update_touch_input_mode_text` next frame.
             }
+            SettingsButton::CycleUiScale => {
+                settings.0.ui_scale = next_ui_scale(settings.0.ui_scale);
+                persist(&path, &settings.0);
+                changed.write(SettingsChangedEvent(settings.0.clone()));
+                // Text refreshed by `update_ui_scale_text`; the live
+                // `bevy::ui::UiScale` resource follows via
+                // `sync_ui_scale_resource` next frame.
+            }
             SettingsButton::ToggleWinnableDealsOnly => {
                 settings.0.winnable_deals_only = !settings.0.winnable_deals_only;
                 persist(&path, &settings.0);