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-core/src/fam_core/app.py

@@ -1,7 +1,7 @@
 """
 FAM-Core 主应用 - Flask 单进程
 
-承载: Task-Scheduler / Dispatcher / Event-Receiver / Chat-Handler / Member-Manager / Video-Server
+承载: Task-Scheduler / Dispatcher / Poller / Event-Receiver / Chat-Handler / Member-Manager / Video-Server
 """
 import os
 import sys
@@ -14,6 +14,7 @@ from .config_loader import load_config
 from .logger import setup_logger
 from .scheduler.scheduler import TaskScheduler
 from .dispatcher.dispatcher import Dispatcher
+from .poller.poller import Poller
 from .event_receiver.event_receiver import event_bp
 from .chat_handler.chat_handler import chat_bp
 from .member_manager.member_manager import member_bp
@@ -37,6 +38,7 @@ def health():
 # 初始化后台线程
 _scheduler = None
 _dispatcher = None
+_poller = None
 
 try:
     _scheduler = TaskScheduler()
@@ -52,6 +54,13 @@ try:
 except Exception as e:
     logger.error(f"Dispatcher 启动失败: {e}")
 
+try:
+    _poller = Poller()
+    _poller.start()
+    logger.info("Poller 已启动")
+except Exception as e:
+    logger.error(f"Poller 启动失败: {e}")
+
 
 @app.route('/api/status', methods=['GET'])
 def status():
@@ -59,6 +68,7 @@ def status():
     return jsonify({
         "scheduler_running": _scheduler._running if _scheduler else False,
         "dispatcher_running": _dispatcher._running if _dispatcher else False,
+        "poller_running": _poller._running if _poller else False,
     }), 200