fix(event-time): event_end_time/frame_timestamp NOT NULL 列兜底

- Edge push 模式: event_end_time 未提供时用 start+视频时长推算
- fam-core db_layer: insert_event 空值兜底(end→start→NOW)
- insert_event_detail: frame_timestamp 空值兜底 NOW
解决 1048 Column cannot be null 落库失败

fam-core/src/fam_core/db_layer.py

@@ -187,12 +187,21 @@ def insert_event(task_id: int, event_start_time: str, event_end_time: str,
     conn = get_conn()
     try:
         cursor = conn.cursor()
+        # event_start/end_time 为 NOT NULL 列: 空值兜底
+        # end 缺失 → 用 start；start 也缺失 → 用当前时间
+        dt_start = _dt_or_none(event_start_time)
+        dt_end = _dt_or_none(event_end_time)
+        if not dt_end:
+            dt_end = dt_start
+        if not dt_start:
+            from datetime import datetime as _dt
+            dt_start = dt_end = _dt.now().strftime('%Y-%m-%d %H:%M:%S')
         cursor.execute(
             """INSERT INTO monitor_events
                (task_id, event_start_time, event_end_time, camera_name,
                 global_summary, entities_json, compute_provider)
                VALUES (%s, %s, %s, %s, %s, %s, %s)""",
-            (task_id, _dt_or_none(event_start_time), _dt_or_none(event_end_time), camera_name,
+            (task_id, dt_start, dt_end, camera_name,
              global_summary, json.dumps(entities_json, ensure_ascii=False),
              json.dumps(compute_provider, ensure_ascii=False))
         )
@@ -214,12 +223,17 @@ def insert_event_detail(event_id: int, task_id: int, frame_index: int,
     conn = get_conn()
     try:
         cursor = conn.cursor()
+        # frame_timestamp 为 NOT NULL 列: 空值兜底为当前时间
+        dt_ts = _dt_or_none(frame_timestamp)
+        if not dt_ts:
+            from datetime import datetime as _dt
+            dt_ts = _dt.now().strftime('%Y-%m-%d %H:%M:%S')
         cursor.execute(
             """INSERT INTO event_details
                (event_id, task_id, frame_index, frame_timestamp, camera_name,
                 person, action, clothing, is_attention_event, source_providers)
                VALUES (%s, %s, %s, %s, %s, %s, %s, %s, %s, %s)""",
-            (event_id, task_id, frame_index, _dt_or_none(frame_timestamp), camera_name,
+            (event_id, task_id, frame_index, dt_ts, camera_name,
              person, action, clothing, is_attention_event,
              json.dumps(source_providers, ensure_ascii=False))
         )