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/tests.rs

@@ -140,6 +140,31 @@ fn pressing_o_toggles_settings_screen_flag() {
     );
 }
 
+/// Esc closes the Settings panel like O / Done do (Phase C dismissal
+/// audit). Esc while the panel is closed must NOT open it.
+#[test]
+fn escape_closes_settings_screen_flag() {
+    let mut app = headless_app();
+
+    press(&mut app, KeyCode::Escape);
+    app.update();
+    assert!(
+        !app.world().resource::<SettingsScreen>().0,
+        "Esc on a closed panel stays closed"
+    );
+
+    press(&mut app, KeyCode::KeyO);
+    app.update();
+    assert!(app.world().resource::<SettingsScreen>().0, "O opens");
+
+    press(&mut app, KeyCode::Escape);
+    app.update();
+    assert!(
+        !app.world().resource::<SettingsScreen>().0,
+        "Esc closes settings"
+    );
+}
+
 // cycle_unlocked pure-function tests
 #[test]
 fn cycle_unlocked_wraps_at_end() {