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/mod.rs

@@ -139,6 +139,10 @@ struct ReduceMotionText;
 #[derive(Component, Debug)]
 struct TouchInputModeText;
 
+/// Marks the `Text` node showing the current UI scale percentage.
+#[derive(Component, Debug)]
+struct UiScaleText;
+
 /// Marks the `Text` node showing the live tooltip-delay value.
 #[derive(Component, Debug)]
 struct TooltipDelayText;
@@ -277,6 +281,10 @@ enum SettingsButton {
     /// (auto-move on tap, default) and `TapToSelect` (first tap selects
     /// a card/stack, second tap on a target pile moves it).
     ToggleTouchInputMode,
+    /// Cycle [`Settings::ui_scale`] through 90 % → 100 % → 115 % →
+    /// 130 % → 90 %. Applied live via `bevy::ui::UiScale`; the table
+    /// stays window-fit (Phase K).
+    CycleUiScale,
     /// Toggle the [`Settings::winnable_deals_only`] flag. When on, new
     /// random Classic-mode deals are filtered through
     /// [`solitaire_core::game_state::GameState::solve_fresh_deal`] until one is provably
@@ -354,6 +362,7 @@ impl SettingsButton {
             SettingsButton::ToggleHighContrast => 61,
             SettingsButton::ToggleReduceMotion => 62,
             SettingsButton::ToggleTouchInputMode => 63,
+            SettingsButton::CycleUiScale => 64,
             // Picker rows — every swatch in a row shares the row's
             // priority so entity-index tiebreaking yields left → right.
             SettingsButton::SelectCardBack(_) => 70,
@@ -449,6 +458,11 @@ impl Plugin for SettingsPlugin {
                     handle_volume_keys,
                     record_window_geometry_changes,
                     persist_window_geometry_after_debounce,
+                    // State sync, not UI — runs even under `headless()`
+                    // so the live `bevy::ui::UiScale` always mirrors the
+                    // setting; rides the mutator spine so it is ordered
+                    // after every settings writer this frame.
+                    sync_ui_scale_resource,
                 )
                     .chain()
                     .in_set(SettingsMutation),
@@ -492,6 +506,7 @@ impl Plugin for SettingsPlugin {
                     update_high_contrast_backgrounds.run_if(resource_changed::<SettingsResource>),
                     update_reduce_motion_text,
                     update_touch_input_mode_text,
+                    update_ui_scale_text,
                     update_tooltip_delay_text,
                     update_time_bonus_multiplier_text,
                     update_replay_move_interval_text,