Turn `dws devapp robot connect` into a 7x24 background service.
- `connect --daemon` re-execs dws into a detached supervisor (POSIX setsid),
prints pid + log path, and exits. Windows is unsupported (stub errors out).
- A supervisor process keeps a worker connector alive, restarting it with
exponential backoff (1s..60s cap, 10 consecutive fast-failure ceiling).
- `connect status` reports running/stale/not-running, pid, uptime and log path.
- `connect stop` sends SIGTERM (worker releases the single-instance lock and
Stream connection), escalates to SIGKILL on a timeout, and cleans the pid file.
- stdout/stderr are archived to ~/.dws/connect/<clientId>/daemon.log via the
existing size-based rotator (new additive logging.NewRotatingFile).
- docs/connect-daemon-service.md ships launchd and systemd templates for
boot-time auto-start.
The single-instance lock (connect_lock.go) is reused unchanged. The foreground
forwarding/session/knowledge logic is untouched; devapp_connect.go only gains
the --daemon flag, two hidden re-exec flags, and the status/stop subcommands.
修雨