DaemonHandle's shutdown_tx (oneshot) is replaced with a CancellationToken
shared between the daemon loop and the IPC server. The token is the
single source of truth for "should we shut down" — `DaemonHandle::shutdown`
cancels it, and an IPC `Stop` request also cancels it.
- daemon/state: store the CancellationToken on DaemonHandle and clone it
on Clone (so cached IPC handles can still trigger shutdown).
- daemon/ipc: IpcServer takes a daemon_shutdown token; `Stop` now cancels
it instead of returning Ok and doing nothing. Add IpcClient with
`request`, `status`, and `stop` methods so the CLI can drive a
backgrounded daemon over the Unix socket.
- daemon/lifecycle: thread the token through run_daemon_loop and
run_session, pass a clone to IpcServer::new.
- lib.rs: re-export IpcClient/IpcCommand/IpcResponse so callers don't
have to reach into the daemon module.
- src/vpn_cmds.rs: `sunbeam disconnect` now actually talks to the daemon
via IpcClient::stop, and `sunbeam vpn status` queries IpcClient::status
and prints addresses + peer count + DERP home.
Sienna Meridian Satterwhite
7019937f6f
