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/events.rs

@@ -56,6 +56,15 @@ pub struct GameWonEvent {
 #[derive(Event, Debug, Clone, Copy)]
 pub struct CardFlippedEvent(pub u32);
 
+/// Fired by the flip animation at its midpoint — the instant the card face
+/// becomes visible (scale.x crosses zero and the phase switches to ScalingUp).
+///
+/// Audio systems should listen to this event rather than `CardFlippedEvent`
+/// so the flip sound is synchronised with the visual reveal, not the move
+/// that triggered the animation.
+#[derive(Event, Debug, Clone, Copy)]
+pub struct CardFaceRevealedEvent(pub u32);
+
 /// Achievement unlocked notification carrying the full `AchievementRecord` for
 /// the newly unlocked achievement. Consumed by the toast renderer and any
 /// persistence/UI systems that need unlock metadata.