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/feedback_anim_plugin.rs

@@ -21,8 +21,8 @@
 //!
 //! # Task #69 — Animated card deal on new game start
 //!
-//! When `NewGameRequestEvent` fires (on a fresh game, `move_count == 0`) or
-//! `NewGameConfirmEvent` fires, `start_deal_anim` reads `LayoutResource` and
+//! When `NewGameRequestEvent` fires (on a fresh game, `move_count == 0`),
+//! `start_deal_anim` reads `LayoutResource` and
 //! inserts a `CardAnim` on every card entity, sliding each card from the stock
 //! pile's position to its current (final) position with a per-card stagger
 //! derived from the current `AnimSpeed` setting plus a deterministic ±10 %