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/leaderboard_plugin.rs

@@ -343,13 +343,21 @@ fn scroll_leaderboard_panel(
     }
 }
 
+/// Done click or Esc dismisses the leaderboard (Phase C dismissal
+/// audit). Esc only fires when the leaderboard is the topmost modal —
+/// with the display-name dialog stacked on top, that dialog owns Esc.
 fn handle_leaderboard_close_button(
     mut commands: Commands,
+    keys: Res<ButtonInput<KeyCode>>,
     close_buttons: Query<&Interaction, (With<LeaderboardCloseButton>, Changed<Interaction>)>,
     screens: Query<Entity, With<LeaderboardScreen>>,
+    other_modal_scrims: Query<(), (With<ModalScrim>, Without<LeaderboardScreen>)>,
     mut closed_flag: ResMut<ClosedThisFrame>,
 ) {
-    if !close_buttons.iter().any(|i| *i == Interaction::Pressed) {
+    let clicked = close_buttons.iter().any(|i| *i == Interaction::Pressed);
+    let esc =
+        keys.just_pressed(KeyCode::Escape) && !screens.is_empty() && other_modal_scrims.is_empty();
+    if !clicked && !esc {
         return;
     }
     for entity in &screens {
@@ -888,12 +896,18 @@ fn handle_display_name_confirm(
 }
 
 /// Discards any typed text and closes the display-name editor modal.
+/// Cancel click or Esc dismisses the display-name dialog without
+/// saving (Phase C dismissal audit — same contract as the sync-setup
+/// dialog's Cancel/Esc pair).
 fn handle_display_name_cancel(
     button_q: Query<&Interaction, (Changed<Interaction>, With<DisplayNameCancelButton>)>,
+    keys: Res<ButtonInput<KeyCode>>,
     screens: Query<Entity, With<DisplayNameModal>>,
     mut commands: Commands,
 ) {
-    if !button_q.iter().any(|i| *i == Interaction::Pressed) {
+    let clicked = button_q.iter().any(|i| *i == Interaction::Pressed);
+    let esc = keys.just_pressed(KeyCode::Escape) && !screens.is_empty();
+    if !clicked && !esc {
         return;
     }
     for entity in &screens {