fix(engine): close Settings, Help, Leaderboard, and theme store on Esc

Phase C dismissal audit: Esc / scrim-tap / Done must behave the same
on every modal. Stragglers found and fixed — none of these had any
Esc path (pause's toggle guard swallowed the key while they were
open):

- Settings: Esc clears SettingsScreen, gated on being the topmost
  modal so a stacked sync-setup / theme-store dialog owns Esc
- Help: Esc closes alongside F1/Done (the code comment already
  claimed an Esc path existed — now it does)
- Leaderboard: Esc closes when topmost; the display-name dialog
  stacked above it now Esc-cancels like sync-setup's dialog
- Theme store: Esc closes (always topmost when open)

Scrim-tap opt-ins are unchanged — ui_modal documents which modals
deliberately stay non-dismissible on outside clicks.

Tests: escape_closes_help_screen, escape_closes_settings_screen_flag.

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

solitaire_engine/src/theme_store_plugin.rs

@@ -118,6 +118,9 @@ impl Plugin for ThemeStorePlugin {
             .init_resource::<CatalogTask>()
             .init_resource::<InstallTask>()
             .init_resource::<StoreBaseUrl>()
+            // Esc-close reads keyboard input; register defensively so
+            // the plugin works under MinimalPlugins in tests.
+            .init_resource::<ButtonInput<KeyCode>>()
             .add_message::<ThemeStoreOpenRequestEvent>()
             .add_message::<InfoToastEvent>()
             .add_message::<WarningToastEvent>()
@@ -344,19 +347,23 @@ fn poll_install_task(
     );
 }
 
-/// Despawns the store modal when Close is pressed.
+/// Despawns the store modal when Close is pressed or on Esc (Phase C
+/// dismissal audit). The store only ever stacks over Settings and
+/// nothing stacks over the store, so it owns Esc whenever it is open
+/// (Settings' own Esc handler is gated on being topmost).
 fn handle_close_button(
     interactions: Query<&Interaction, (Changed<Interaction>, With<ThemeStoreCloseButton>)>,
+    keys: Res<ButtonInput<KeyCode>>,
     screens: Query<Entity, With<ThemeStoreScreen>>,
     mut commands: Commands,
 ) {
-    for interaction in &interactions {
-        if *interaction != Interaction::Pressed {
-            continue;
-        }
-        for entity in &screens {
-            commands.entity(entity).despawn();
-        }
+    let clicked = interactions.iter().any(|i| *i == Interaction::Pressed);
+    let esc = keys.just_pressed(KeyCode::Escape) && !screens.is_empty();
+    if !clicked && !esc {
+        return;
+    }
+    for entity in &screens {
+        commands.entity(entity).despawn();
     }
 }