feat(notify): 推送通知接入飞书 Webhook

新增 webhook_adapter 飞书群机器人推送 (含签名校验);preferences/settings
增加 feishu_webhook_url/secret 与 webhook_enabled_default (新建规则默认推送)
配置与端点;Monitoring 设置页重构为「推送通知」卡片 (渠道列表+飞书地址折叠
+默认渠道勾选);RuleEditor 规则编辑器支持单条规则勾选飞书。
QMT/ptrade 渠道文案统一改为「待定」。

backend/app/api/monitor_rules.py

@@ -47,7 +47,7 @@ class RuleModel(BaseModel):
     logic: str = "and"        # and | or
     cooldown_seconds: int = 3600
     severity: str = "info"    # info | warn | critical
-    webhook_url: str = ""     # Webhook 推送地址 (推送到 QMT 等外部软件, 开发中)
+    webhook_url: str = ""     # Webhook 推送地址 (推送到 QMT 等外部软件, 待定)
     webhook_enabled: bool = False
     message: str = ""