Enhance ball rings with neon glow effect (additive blending)

app.py

@@ -1231,7 +1231,10 @@ def _build_ball_trail_mask(state: AppState, frame_idx: int) -> np.ndarray | None
     if kick_candidate is None:
         return None
 
-    start_idx = max(int(kick_candidate) + 1, int(frame_idx) + 1)
+    if int(frame_idx) <= int(kick_candidate):
+        start_idx = int(kick_candidate) + 1
+    else:
+        start_idx = max(int(kick_candidate) + 1, int(frame_idx))
     end_idx = state.num_frames
     if start_idx >= end_idx:
         return None