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/events.rs

@@ -29,6 +29,13 @@ pub struct UndoRequestEvent;
 pub struct NewGameRequestEvent {
     pub seed: Option<u64>,
     pub mode: Option<GameMode>,
+    /// `true` when this request originated from the user confirming the
+    /// abandon-current-game modal (Y / Enter on `ConfirmNewGameScreen`).
+    /// `handle_new_game` skips spawning the dialog when this is set,
+    /// otherwise it would respawn the modal in the frame after the player
+    /// presses Y (the despawn-on-Y has flushed by then) and the new game
+    /// would never actually start.
+    pub confirmed: bool,
 }
 
 /// Fired by `GamePlugin` after any successful state mutation. Rendering and