feat(engine): N keypress now opens the real Confirm/Cancel modal

Previously a first N press during an active game showed a "Press N
again" toast and started a 3-second countdown — a UI-first violation
since the only continuation was another keystroke. The HUD New Game
button already routed through `ConfirmNewGameScreen` with real Cancel
/ New game buttons; this change makes keyboard N do the same.

- handle_keyboard_core fires NewGameRequestEvent::default() directly;
  handle_new_game's existing active-game check spawns the modal.
- Shift+N keeps the keyboard power-user bypass (confirmed: true).
- N is suppressed while the confirm modal or restore prompt is open
  so those modals' own input handlers can process N (cancel /
  start-new-game) without us re-firing the same frame they close.
- KeyboardConfirmState, NEW_GAME_CONFIRM_WINDOW, NewGameConfirmEvent,
  and the "Press N again" toast handler are removed.

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

solitaire_engine/src/lib.rs

@@ -88,7 +88,7 @@ pub use events::{
     AchievementUnlockedEvent, CardFaceRevealedEvent, CardFlippedEvent, DrawRequestEvent,
     ForfeitEvent, ForfeitRequestEvent, FoundationCompletedEvent, GameWonEvent, HelpRequestEvent,
     HintVisualEvent, InfoToastEvent, ManualSyncRequestEvent, MoveRejectedEvent, MoveRequestEvent,
-    NewGameConfirmEvent, NewGameRequestEvent, PauseRequestEvent, StartChallengeRequestEvent,
+    NewGameRequestEvent, PauseRequestEvent, StartChallengeRequestEvent,
     StartDailyChallengeRequestEvent, StartTimeAttackRequestEvent, StartZenRequestEvent,
     StateChangedEvent, SyncCompleteEvent, ToggleAchievementsRequestEvent,
     ToggleLeaderboardRequestEvent, ToggleProfileRequestEvent, ToggleSettingsRequestEvent,