Replace attempt_ws_connect() with attempt_tcp_probe() in RemoteManager to
avoid allocating per-connection resources (PtyManager, SidecarManager) on
the relay during reconnection probes. Add onRemoteMachineReconnecting and
onRemoteMachineReconnectReady event listeners in remote-bridge.ts. Wire
machines store to auto-reconnect when relay becomes reachable.
remote-bridge.ts adapter for machine management IPC. machines.svelte.ts
store for remote machine state. Layout store extended with
remoteMachineId on Pane interface. agent-bridge.ts and pty-bridge.ts
route to remote commands when remoteMachineId is set. SettingsDialog
gains Remote Machines section. Sidebar auto-groups remote panes by
machine label.