fix(aiot): 添加离岗检测算法的离岗倒计时参数

- 添加 leave_countdown_sec 参数到离岗检测算法 schema
- 默认值：300秒（5分钟）
- 作用：确认离岗后，倒计时结束才触发告警
- 与 confirm_leave_sec（离岗确认）和 cooldown_sec（告警冷却）区分

算法流程：
1. 持续离开 confirm_leave_sec（30秒）→ 确认离岗
2. 倒计时 leave_countdown_sec（300秒）→ 触发告警
3. 告警后 cooldown_sec（600秒）内不再重复告警

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

src/main/java/com/genersoft/iot/vmp/aiot/service/impl/AiAlgorithmServiceImpl.java

@@ -41,7 +41,7 @@ public class AiAlgorithmServiceImpl implements IAiAlgorithmService {
         // algoCode -> {algoName, targetClass, description, paramSchema}
         PRESET_ALGORITHMS.put("leave_post", new String[]{
                 "离岗检测", "person", "检测人员是否在岗，支持工作时间段配置",
-                "{\"confirm_on_duty_sec\":{\"type\":\"int\",\"default\":10,\"min\":1},\"confirm_leave_sec\":{\"type\":\"int\",\"default\":30,\"min\":1},\"cooldown_sec\":{\"type\":\"int\",\"default\":600,\"min\":0},\"working_hours\":{\"type\":\"list\",\"default\":[]}}"
+                "{\"confirm_on_duty_sec\":{\"type\":\"int\",\"default\":10,\"min\":1},\"confirm_leave_sec\":{\"type\":\"int\",\"default\":30,\"min\":1},\"leave_countdown_sec\":{\"type\":\"int\",\"default\":300,\"min\":0},\"cooldown_sec\":{\"type\":\"int\",\"default\":600,\"min\":0},\"working_hours\":{\"type\":\"list\",\"default\":[]}}"
         });
         PRESET_ALGORITHMS.put("intrusion", new String[]{
                 "周界入侵检测", "person", "检测人员进入指定区域",