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.
- Default BIND_SOURCE_IP=false: do not pin inet4_bind_address (stale
source IP after WWAN re-dial was the main rep=0x01 cause).
- Add scripts/watch-cellular.sh: ip monitor events + poll, regenerate
when iface missing or pinned source IP drifts.
- systemd: cellular-proxy-watch.service + 2min timer oneshot fallback.
- cpxy watch {status|once|start|stop|logs}
- Install/upgrade enable watch when ENABLE_CELLULAR_WATCH=true.
Hermes