feat(exercise): 优化死虫式训练姿态检测算法

- 调整视频处理频率从每帧处理改为每2帧处理
- 添加膝角趋势平滑算法减少单帧抖动误判
- 改进对角伸展检测逻辑支持准备位手臂上举
- 优化状态机确保严格回到准备姿态才计数
- 添加姿态丢失时的候选帧清理机制
- 更新音频文件生成路径至resources目录
- 改进macOS音频生成使用AIFF格式提高质量
- 添加详细的帧处理日志输出间隔配置

app/exercises/dead_bug/detector.py

@@ -110,6 +110,7 @@ class DeadBugDetector:
         annotated = bgr_frame.copy()
 
         if pose_result is None or not pose_result.pose_landmarks:
+            self._state.mark_no_pose()
             result = DeadBugResult(
                 rep_count=self._state.rep_count,
                 phase=DeadBugPhase.NO_POSE,
@@ -125,6 +126,7 @@ class DeadBugDetector:
         draw_landmarks(annotated, landmarks, REQUIRED_LANDMARKS, visibility_threshold=self.visibility_threshold)
 
         if not has_required_visibility(landmarks, REQUIRED_LANDMARKS, self.visibility_threshold):
+            self._state.mark_no_pose()
             result = DeadBugResult(
                 rep_count=self._state.rep_count,
                 phase=DeadBugPhase.NO_POSE,