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/input_plugin.rs

@@ -183,6 +183,7 @@ fn handle_keyboard_core(
                 ev.new_game.write(NewGameRequestEvent {
                     seed: None,
                     mode: Some(solitaire_core::game_state::GameMode::Classic),
+                    confirmed: false,
                 });
                 confirm.new_game_countdown = 0.0;
                 return;
@@ -218,6 +219,7 @@ fn handle_keyboard_core(
             ev.new_game.write(NewGameRequestEvent {
                 seed: None,
                 mode: Some(solitaire_core::game_state::GameMode::Zen),
+                confirmed: false,
             });
         } else {
             ev.info_toast.write(InfoToastEvent(format!(