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_data/src/settings.rs

@@ -275,6 +275,14 @@ pub struct Settings {
     /// which marks the tip as unnecessary without showing it.
     #[serde(default)]
     pub shown_radial_menu_tip: bool,
+    /// Global UI scale multiplier applied to all UI chrome (HUD, modals,
+    /// action bar) — the table itself stays window-fit via
+    /// `compute_layout`. Cycles through 0.9 / 1.0 / 1.15 / 1.3 in
+    /// Settings → Accessibility; clamped to `[UI_SCALE_MIN,
+    /// UI_SCALE_MAX]` by [`Settings::sanitized`]. Older `settings.json`
+    /// files deserialize cleanly to `1.0` via the serde default.
+    #[serde(default = "default_ui_scale")]
+    pub ui_scale: f32,
     /// Custom public name displayed on the leaderboard. When `None`, the
     /// player's server `username` is used instead. Trimmed to 32 characters
     /// before submission. Older `settings.json` files written before this
@@ -383,6 +391,16 @@ fn default_replay_move_interval_secs() -> f32 {
     0.45
 }
 
+/// Lowest / highest UI scale the settings row offers; anything outside
+/// (hand-edited settings.json) clamps here on load.
+pub const UI_SCALE_MIN: f32 = 0.9;
+/// See [`UI_SCALE_MIN`].
+pub const UI_SCALE_MAX: f32 = 1.3;
+
+fn default_ui_scale() -> f32 {
+    1.0
+}
+
 fn default_matomo_site_id() -> u32 {
     1
 }
@@ -446,6 +464,7 @@ impl Default for Settings {
             last_seen_whats_new: String::new(),
             shown_stall_hint_tip: false,
             shown_radial_menu_tip: false,
+            ui_scale: default_ui_scale(),
             leaderboard_display_name: None,
             leaderboard_opted_in: false,
             take_from_foundation: true,
@@ -481,6 +500,7 @@ impl Settings {
             replay_move_interval_secs: self
                 .replay_move_interval_secs
                 .clamp(REPLAY_MOVE_INTERVAL_MIN_SECS, REPLAY_MOVE_INTERVAL_MAX_SECS),
+            ui_scale: self.ui_scale.clamp(UI_SCALE_MIN, UI_SCALE_MAX),
             selected_theme_id,
             ..self
         }