Ping-pong turns on the last key, and stepped rows hold the key they last passed (#112)

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

src/runtime/systems/AnimationSystem.ts

@@ -59,7 +59,7 @@ export class AnimationSystem implements System {
       } else if (player.playing && isHandleEnabled(entity)) player.time += dt;
       const head = animationPlayheadAt(asset, player.time);
       for (const b of bindings) {
-        const value = trackWriteAt(b.track, b.kind, head.frame, player.bases[b.base]);
+        const value = trackWriteAt(b.track, b.kind, head.frame, player.bases[b.base], head.reverse);
         if (value !== undefined) b.write(value);
       }
       if (!head.finished) continue;