fix: Edge端三处修复 — API key丢失致全模型失败 + 失败结果黑洞 + 重派发死锁

根因: Edge服务手动重启未source .env，GEMINI/NVIDIA key丢失，
所有视觉模型调用失败("All models failed")，且失败结果永不回传NAS。

1. config_loader: 启动时自动加载.env(export KEY=VALUE)，已存在环境变量不覆盖
2. queue_manager.enqueue: FAILED(或已交付SUCCESS)行重置为PENDING复用重跑，
   修复 INSERT OR IGNORE + UNIQUE(nas_task_id) 导致的静默忽略死锁
3. get_undelivered_results: 包含FAILED状态，/results构造failed负载，
   NAS Poller可感知失败避免僵尸循环空转重传
4. ddl.sql: failure_stage ENUM 增加 'process'(与db_layer valid_stages对齐)，
   修复 pymysql DataError 1265

验证: task 293(压缩后22MB) NVIDIA降级分析成功→event_id=13；
task 295 全链路成功→event_id=14；NAS端ENUM已同步ALTER

fam-edge/src/fam_edge/queue/queue_manager.py

@@ -73,9 +73,24 @@ def enqueue(nas_task_id: int, video_filename: str, video_path: str,
         conn.commit()
         if cur.rowcount == 0:
             row = conn.execute(
-                "SELECT id FROM task_queue WHERE nas_task_id=?", (nas_task_id,)
+                "SELECT id, status, delivered FROM task_queue WHERE nas_task_id=?",
+                (nas_task_id,)
             ).fetchone()
-            return row['id'] if row else 0
+            if row is None:
+                return 0
+            # NAS 重新派发: FAILED（或已交付的 SUCCESS）重置为 PENDING，用新上传的视频重跑。
+            # SUCCESS 且未交付的行不动，避免丢失待 Poller 拉取的结果。
+            if row['status'] == 'FAILED' or (row['status'] == 'SUCCESS' and row['delivered']):
+                conn.execute(
+                    "UPDATE task_queue SET status='PENDING', result_json=NULL, error_message=NULL, "
+                    "failure_stage=NULL, retry_count=0, delivered=0, video_filename=?, video_path=?, "
+                    "camera_name=?, event_start_time=?, known_members_context=?, "
+                    "updated_at=datetime('now','localtime') WHERE id=?",
+                    (video_filename, video_path, camera_name, event_start_time,
+                     known_members_context, row['id'])
+                )
+                conn.commit()
+            return row['id']
         return cur.lastrowid
     finally:
         conn.close()
@@ -132,8 +147,10 @@ def mark_failed(task_id: int, error_message: str, failure_stage: str = ''):
 def get_undelivered_results(limit: int = 10) -> List[Dict]:
     conn = _get_conn()
     try:
+        # FAILED 也需交付: 否则 NAS 永远收不到失败结果，任务卡 PROCESSING
+        # 直至僵尸回收后无意义地重传 22MB 视频
         rows = conn.execute(
-            "SELECT * FROM task_queue WHERE status='SUCCESS' AND delivered=0 "
+            "SELECT * FROM task_queue WHERE status IN ('SUCCESS','FAILED') AND delivered=0 "
             "ORDER BY id LIMIT ?", (limit,)
         ).fetchall()
         return [dict(r) for r in rows]
@@ -166,7 +183,8 @@ def get_queue_stats() -> Dict:
             ).fetchone()
             stats[status] = row['cnt']
         row = conn.execute(
-            "SELECT COUNT(*) as cnt FROM task_queue WHERE status='SUCCESS' AND delivered=0"
+            "SELECT COUNT(*) as cnt FROM task_queue "
+            "WHERE status IN ('SUCCESS','FAILED') AND delivered=0"
         ).fetchone()
         stats['UNDELIVERED'] = row['cnt']
         return stats