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/settings_plugin/input.rs

@@ -50,15 +50,21 @@ pub(super) fn handle_volume_keys(
 }
 
 /// Opens or closes the Settings panel — `O` keyboard accelerator or
-/// `ToggleSettingsRequestEvent` from the HUD Menu popover.
+/// `ToggleSettingsRequestEvent` from the HUD Menu popover. Esc closes
+/// too (Phase C dismissal audit), but only when Settings is the
+/// topmost modal — with sync-setup or the theme store stacked on top,
+/// the stacked dialog owns Esc.
 pub(super) fn toggle_settings_screen(
     keys: Res<ButtonInput<KeyCode>>,
     mut requests: MessageReader<ToggleSettingsRequestEvent>,
     mut screen: ResMut<SettingsScreen>,
+    other_modal_scrims: Query<(), (With<ModalScrim>, Without<SettingsPanel>)>,
 ) {
     let button_clicked = requests.read().count() > 0;
     if keys.just_pressed(KeyCode::KeyO) || button_clicked {
         screen.0 = !screen.0;
+    } else if keys.just_pressed(KeyCode::Escape) && screen.0 && other_modal_scrims.is_empty() {
+        screen.0 = false;
     }
 }