feat(engine): MoveRejectedEvent + PausePlugin (Esc)

- New MoveRejectedEvent fires from end_drag when the cursor is over
  a real pile but the placement is illegal. AudioPlugin plays
  card_invalid.wav on it.
- New PausePlugin + PausedResource: Esc toggles a full-window
  overlay and the flag. tick_elapsed_time and advance_time_attack
  skip work while paused. Help cheat sheet updated.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

solitaire_engine/src/time_attack_plugin.rs

@@ -79,10 +79,14 @@ fn advance_time_attack(
     time: Res<Time>,
     mut session: ResMut<TimeAttackResource>,
     mut ended: EventWriter<TimeAttackEndedEvent>,
+    paused: Option<Res<crate::pause_plugin::PausedResource>>,
 ) {
     if !session.active {
         return;
     }
+    if paused.is_some_and(|p| p.0) {
+        return;
+    }
     session.remaining_secs -= time.delta_secs();
     if session.remaining_secs <= 0.0 {
         let wins = session.wins;