feat: 异步任务队列架构 - SQLite队列 + 速率限制 + NAS Poller

Edge端:
- 新增 SQLite 异步任务队列 (queue_manager + consumer)
- 新增 TokenBucket 速率限制器 (Gemini 1000 RPM, NVIDIA 40 RPM, burst 2x)
- 新增 /api/edge/video/enqueue + /api/edge/results 端点
- 消费者线程从队列消费任务，按速率限制调用AI模型
- orchestrator 集成 rate_limiter，Gemini优先→NVIDIA兜底

NAS端:
- Dispatcher 重构为 enqueue 模式（上传后立即返回，不等结果）
- 新增 Poller 线程（定期从Edge拉取结果写 MariaDB）
- app.py 启动 Poller，config.yaml 新增 poller 配置
- db_layer 更新 valid_stages 添加 'process'

fam-edge/src/fam_edge/api_gateway/api_gateway.py

@@ -1,8 +1,12 @@
 """
 API-Gateway - Flask 蓝图，接收任务
 
-同时只允许 1 个任务在处理；新任务到达时若当前有任务处理中，返回 429
+模式:
+1. enqueue (异步): NAS 上传视频 → Edge 入队 → 立即返回 → 消费者异步处理 → NAS 轮询拉取结果
+2. push (同步, 兼容保留): NAS 上传 → Edge 同步处理 → 结果随响应返回
+3. analyze (旧拉取模式, 兼容保留)
 """
+import os
 import threading
 import requests
 from flask import Blueprint, request, jsonify
@@ -10,12 +14,12 @@ from flask import Blueprint, request, jsonify
 from ..logger import setup_logger
 from ..ai_orchestrator.orchestrator import AIOrchestrator
 from ..video_preprocessor.preprocessor import VideoPreprocessor
+from ..queue import queue_manager
 
 logger = setup_logger('fam-edge.api_gateway')
 
 api_bp = Blueprint('api_gateway', __name__)
 
-# 并发控制：同时只允许 1 个任务
 _current_task_lock = threading.Lock()
 _currently_processing = False
 
@@ -72,6 +76,92 @@ def receive_task():
     return jsonify({"status": "accepted", "task_id": task_id}), 202
 
 
+@api_bp.route('/api/edge/video/enqueue', methods=['POST'])
+def enqueue_task():
+    """异步模式：接收 multipart 视频上传，入队后立即返回
+
+    NAS 上传视频 → Edge 保存到磁盘 + 入 SQLite 队列 → 返回 task_id
+    消费者线程异步处理，NAS 通过 /api/edge/results 拉取结果
+    """
+    task_id_raw = request.form.get('task_id')
+    file = request.files.get('video')
+    if not task_id_raw or not file:
+        return jsonify({"error": "缺少必填字段: task_id, video"}), 400
+
+    try:
+        task_id = int(task_id_raw)
+    except ValueError:
+        return jsonify({"error": "task_id 必须是整数"}), 400
+
+    camera_name = request.form.get('camera_name', '')
+    event_start_time = request.form.get('event_start_time', '')
+    known_members_context = request.form.get('known_members_context', '')
+
+    upload_dir = os.environ.get('FAM_UPLOAD_DIR', '/tmp/fam_uploads')
+    os.makedirs(upload_dir, exist_ok=True)
+    video_filename = f"task_{task_id}_{file.filename}"
+    video_path = os.path.join(upload_dir, video_filename)
+
+    try:
+        file.save(video_path)
+        size_mb = os.path.getsize(video_path) / 1024 / 1024
+        logger.info(f"[task_id={task_id}] 入队: {file.filename} ({size_mb:.1f}MB)")
+
+        queue_id = queue_manager.enqueue(
+            nas_task_id=task_id,
+            video_filename=file.filename,
+            video_path=video_path,
+            camera_name=camera_name,
+            event_start_time=event_start_time,
+            known_members_context=known_members_context,
+        )
+
+        return jsonify({
+            "status": "queued",
+            "task_id": task_id,
+            "queue_id": queue_id,
+        }), 202
+
+    except Exception as e:
+        logger.error(f"[task_id={task_id}] 入队失败: {e}", exc_info=True)
+        if os.path.exists(video_path):
+            os.remove(video_path)
+        return jsonify({"error": str(e)}), 500
+
+
+@api_bp.route('/api/edge/results', methods=['GET'])
+def get_results():
+    """返回已完成但未拉取的结果，标记为已交付"""
+    limit = int(request.args.get('limit', 10))
+    results = queue_manager.get_undelivered_results(limit=limit)
+
+    import json
+    payload = []
+    task_ids = []
+    for r in results:
+        try:
+            result_json = json.loads(r['result_json']) if r['result_json'] else None
+        except json.JSONDecodeError:
+            result_json = None
+        payload.append({
+            "nas_task_id": r['nas_task_id'],
+            "result": result_json,
+        })
+        task_ids.append(r['id'])
+
+    if task_ids:
+        queue_manager.mark_delivered(task_ids)
+
+    return jsonify({"results": payload, "count": len(payload)}), 200
+
+
+@api_bp.route('/api/edge/queue/stats', methods=['GET'])
+def queue_stats():
+    """队列状态统计"""
+    stats = queue_manager.get_queue_stats()
+    return jsonify(stats), 200
+
+
 @api_bp.route('/api/edge/video/push', methods=['POST'])
 def receive_push_task():
     """推送模式：接收 multipart 视频上传，同步分析，结果随 HTTP 响应返回