feat(engine): require N-key confirmation when abandoning an active game

Pressing N during an active game (move_count > 0, not won) now shows a
"Press N again to start a new game" toast and only starts a new game if
N is pressed a second time within 3 seconds. Starting a fresh game or
pressing N after a win still acts immediately.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

solitaire_engine/src/lib.rs

@@ -40,7 +40,8 @@ pub use audio_plugin::{AudioPlugin, AudioState, SoundLibrary};
 pub use card_plugin::{CardEntity, CardLabel, CardPlugin};
 pub use events::{
     AchievementUnlockedEvent, CardFlippedEvent, DrawRequestEvent, GameWonEvent, ManualSyncRequestEvent,
-    MoveRejectedEvent, MoveRequestEvent, NewGameRequestEvent, StateChangedEvent, UndoRequestEvent,
+    MoveRejectedEvent, MoveRequestEvent, NewGameConfirmEvent, NewGameRequestEvent, StateChangedEvent,
+    UndoRequestEvent,
 };
 pub use game_plugin::{GameMutation, GamePlugin, GameStatePath};
 pub use help_plugin::{HelpPlugin, HelpScreen};