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/animation_plugin.rs

@@ -21,7 +21,7 @@ use crate::card_animation::{sample_curve, CardAnimation, MotionCurve};
 use crate::card_plugin::CardEntity;
 use crate::challenge_plugin::ChallengeAdvancedEvent;
 use crate::daily_challenge_plugin::{DailyChallengeCompletedEvent, DailyGoalAnnouncementEvent};
-use crate::events::{InfoToastEvent, NewGameConfirmEvent, XpAwardedEvent};
+use crate::events::{InfoToastEvent, XpAwardedEvent};
 use crate::events::{AchievementUnlockedEvent, GameWonEvent};
 use crate::game_plugin::GameMutation;
 use crate::layout::LayoutResource;
@@ -161,7 +161,6 @@ impl Plugin for AnimationPlugin {
             .add_message::<TimeAttackEndedEvent>()
             .add_message::<ChallengeAdvancedEvent>()
             .add_message::<SettingsChangedEvent>()
-            .add_message::<NewGameConfirmEvent>()
             .add_message::<InfoToastEvent>()
             .add_message::<XpAwardedEvent>()
             .init_resource::<EffectiveSlideDuration>()
@@ -183,7 +182,6 @@ impl Plugin for AnimationPlugin {
                     handle_challenge_toast,
                     handle_settings_toast,
                     handle_auto_complete_toast,
-                    handle_new_game_confirm_toast,
                     handle_xp_awarded_toast,
                     tick_toasts,
                     (enqueue_toasts, drive_toast_display).chain(),
@@ -459,15 +457,6 @@ fn handle_auto_complete_toast(
     }
 }
 
-fn handle_new_game_confirm_toast(
-    mut commands: Commands,
-    mut events: MessageReader<NewGameConfirmEvent>,
-) {
-    for _ in events.read() {
-        spawn_toast(&mut commands, "Press N again to start a new game".to_string(), 3.0);
-    }
-}
-
 /// Reads every incoming `InfoToastEvent` and appends its text to `ToastQueue`.
 ///
 /// This is the first half of the two-system toast queue (Task #67). The queue