fix(engine): start new game when player confirms abandon-current-game modal

Reported during 2026-04-29 smoke test: pressing Y on the
ConfirmNewGameScreen modal closed nothing and didn't start a new game.

Trace:
  Frame N: handle_confirm_input despawns the modal entity (deferred),
           writes NewGameRequestEvent.
  End of N: command flush — modal gone.
  Frame N+1: handle_new_game reads the event. needs_confirm is still
             true (game state unchanged). confirm_already_open is now
             false (modal flushed). Condition matches → spawn_confirm_
             dialog runs again, the modal reappears, and the new game
             never starts.

Add a `confirmed: bool` field to NewGameRequestEvent. handle_confirm_
input writes it as true on Y/Enter so handle_new_game's dialog-spawn
guard short-circuits and the existing despawn-and-start branch runs.
All other writers (button click, N hotkey, mode hotkeys, daily/
challenge/time-attack auto-deal, tests) stay at `confirmed: false`.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

solitaire_engine/src/win_summary_plugin.rs

@@ -742,6 +742,7 @@ mod tests {
         app.world_mut().write_message(NewGameRequestEvent {
             seed: None,
             mode: Some(GameMode::Zen),
+            confirmed: false,
         });
         app.update();