feat: 离岗算法滑动窗口抗抖动优化

- 上岗确认阈值从 0.7 降为 0.6，降低漏确认
- 离岗触发从 ratio==0 改为 ratio<0.2，允许 20% 抖动
- 离岗中断从单帧判断改为 ratio>=0.5，避免偶尔一帧误检打断确认
- 入侵算法不变，通过调高 conf 到 0.6 解决误报

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

algorithms.py

@@ -241,7 +241,7 @@ class LeavePostAlgorithm:
                 self.state_start_time = current_time
                 self.detection_window.clear()
                 logger.debug(f"ROI {roi_id}: CONFIRMING_ON_DUTY → INIT (人消失)")
-            elif elapsed >= self.confirm_on_duty_sec and detection_ratio >= 0.7:
+            elif elapsed >= self.confirm_on_duty_sec and detection_ratio >= 0.6:
                 # 上岗确认成功（命中率>=70%）
                 self.state = self.STATE_ON_DUTY
                 self.state_start_time = current_time
@@ -250,8 +250,8 @@ class LeavePostAlgorithm:
 
         elif self.state == self.STATE_ON_DUTY:
             # 在岗状态：监控是否离岗
-            if detection_ratio == 0:
-                # 滑动窗口内完全没有人，进入离岗确认
+            if detection_ratio < 0.2:
+                # 滑动窗口内 80% 以上帧无人，进入离岗确认
                 self.state = self.STATE_CONFIRMING_OFF_DUTY
                 self.state_start_time = current_time
                 logger.debug(f"ROI {roi_id}: ON_DUTY → CONFIRMING_OFF_DUTY")
@@ -260,12 +260,12 @@ class LeavePostAlgorithm:
             # 离岗确认中：需要持续未检测到人
             elapsed = (current_time - self.state_start_time).total_seconds()
 
-            if roi_has_person:
-                # 人回来了，回到ON_DUTY
+            if detection_ratio >= 0.5:
+                # 窗口内检测率恢复到 50% 以上，人确实回来了
                 self.state = self.STATE_ON_DUTY
                 self.state_start_time = current_time
-                logger.debug(f"ROI {roi_id}: CONFIRMING_OFF_DUTY → ON_DUTY (人回来了)")
-            elif elapsed >= self.confirm_off_duty_sec and detection_ratio == 0:
+                logger.debug(f"ROI {roi_id}: CONFIRMING_OFF_DUTY → ON_DUTY (人回来了, ratio={detection_ratio:.2f})")
+            elif elapsed >= self.confirm_off_duty_sec and detection_ratio < 0.2:
                 # 离岗确认成功，进入倒计时
                 self.state = self.STATE_OFF_DUTY_COUNTDOWN
                 self.state_start_time = current_time