feat(engine): playability improvements — rounds 7–9 (#40–#64)

Round 7 — Input & feedback
- H key cycles hints; F1 opens help (conflict resolved)
- N key cancels active Time Attack session
- Hint text distinguishes "draw from stock" vs "recycle waste"
- Forfeit (G) clears AutoCompleteState so chime does not bleed into new deal
- Zen mode timer clears immediately on Z press
- HUD shows recycle count in both draw modes
- Settings scroll position persisted across open/close

Round 8 — Polish & clarity
- Undo unavailable fires "Nothing to undo" toast
- Streak-break toast on forfeit/abandon when streak > 1
- F11 fullscreen toggle with toast; documented in help and home screens
- H-after-win, new-game countdown expiry, Tab-no-cards toasts
- Win cascade duration/stagger scales with animation speed setting
- Draw-Three cycle counter HUD ("Cycle: N/3")
- Forfeit requires G×2 confirmation within 3 s (mirrors N key)

Round 9 — Game feel & information
- Escape dismisses game-over/stuck overlay (PausePlugin skips Escape when overlay visible)
- Shake animation on rejected drag before snap-back
- Forfeit countdown cancels when any other key is pressed (U/H/D/Z/Space)
- Tab wrap-around fires "Back to first card" toast
- HUD selection indicator shows active Tab-selected pile in yellow
- Challenge time-limit HUD turns orange < 60s, red < 30s
- Win summary shows XP breakdown (+50 base, +25 no-undo, +N speed)
- Game-over overlay: "No more moves available" with clear N/Escape/G instructions

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

solitaire_engine/src/challenge_plugin.rs

@@ -44,6 +44,7 @@ fn advance_on_challenge_win(
     mut progress: ResMut<ProgressResource>,
     path: Res<ProgressStoragePath>,
     mut advanced: EventWriter<ChallengeAdvancedEvent>,
+    mut toast: EventWriter<InfoToastEvent>,
 ) {
     for _ in wins.read() {
         if game.0.mode != GameMode::Challenge {
@@ -56,6 +57,9 @@ fn advance_on_challenge_win(
                 warn!("failed to save progress after challenge advance: {e}");
             }
         }
+        // Human-readable level is 1-based (index 0 → "Challenge 1").
+        let level_number = prev.saturating_add(1);
+        toast.send(InfoToastEvent(format!("Challenge {level_number} complete!")));
         advanced.send(ChallengeAdvancedEvent {
             previous_index: prev,
             new_index: progress.0.challenge_index,
@@ -199,6 +203,48 @@ mod tests {
         assert_eq!(challenge_progress_label(2), format!("3 / {total}"));
     }
 
+    #[test]
+    fn challenge_win_fires_complete_toast_with_level_number() {
+        let mut app = headless_app();
+        // Set challenge_index to 2 so the completed level is "Challenge 3".
+        app.world_mut().resource_mut::<ProgressResource>().0.challenge_index = 2;
+        app.world_mut().resource_mut::<GameStateResource>().0 =
+            GameState::new_with_mode(1, DrawMode::DrawOne, GameMode::Challenge);
+
+        app.world_mut().send_event(GameWonEvent {
+            score: 500,
+            time_seconds: 100,
+        });
+        app.update();
+
+        let events = app.world().resource::<Events<InfoToastEvent>>();
+        let mut cursor = events.get_cursor();
+        let fired: Vec<_> = cursor.read(events).collect();
+        assert_eq!(fired.len(), 1, "exactly one toast must fire on challenge win");
+        assert!(
+            fired[0].0.contains("Challenge 3"),
+            "toast must name the 1-based level that was just completed"
+        );
+    }
+
+    #[test]
+    fn classic_win_does_not_fire_challenge_complete_toast() {
+        let mut app = headless_app();
+        // Default mode is Classic.
+        app.world_mut().send_event(GameWonEvent {
+            score: 500,
+            time_seconds: 100,
+        });
+        app.update();
+
+        let events = app.world().resource::<Events<InfoToastEvent>>();
+        let mut cursor = events.get_cursor();
+        assert!(
+            cursor.read(events).next().is_none(),
+            "no challenge toast should fire for non-Challenge wins"
+        );
+    }
+
     #[test]
     fn pressing_x_below_unlock_level_fires_info_toast() {
         let mut app = headless_app();