feat(watch): treat ModemManager journal as redial standard

Use MM registration/packet-service events as the recovery trigger
instead of public egress probes, so re-register heals with zero
cellular traffic. Wait for wwan IPv4 after settle, coalesce bursts,
and keep ip-monitor + poll as fallbacks.

docs/ops.md

@@ -6,6 +6,17 @@
 2. 需要「用流量出口」时：把应用的 HTTP/SOCKS 指到 `LAN:7890`  
 3. `cpxy verify` 确认代理 IP ≠ 直连 IP  
 
+## 重拨检测（ModemManager 日志标准）
+
+watch 默认以 **本机 ModemManager journal** 作为「数据网络重拨/重注册」信号，**不消耗蜂窝公网流量**：
+
+- 典型命中：`registration state changed (home -> searching)`、`packet service state changed (attached -> detached)`、bearer 断连、access tech 抖动
+- 动作：`WATCH_MM_SETTLE_SEC` 后等待 `wwan` IPv4（可选 mmcli home），再 `generate/restart` 清半开连接
+- 同一轮抖动用 `WATCH_MM_COALESCE_SEC` 合并，避免连刷三次
+- 首次启动写 `mm.cursor`，**不回放历史日志**，避免升级后误 rebind
+- 相关日志：`/var/log/cellular-proxy/watch.log`、`mm.last_event`、`watch.state`
+- 关闭：`WATCH_MM_EVENTS=false` 后 `systemctl restart cellular-proxy-watch`  
+
 ## 内存
 
 ```bash