Generalize the daemon's PTY spawn so a session can target either the node's host
shell (today) or `docker exec -it <container> tmux …` (the node-placed agent
terminal, which shares the container's node-local ~/drives). A `container` (+
optional `session`) field on pty_open/webrtc_offer selects the container path;
absent it, the host shell path is byte-identical to before — so the Infra node
terminal is unaffected. Threads PtyTarget through open_pty + rtc handle_offer →
build_peer → bridge_pty. Additive; nothing emits `container` yet.
Co-Authored-By: Claude Opus 4.8 (1M context) <[email protected]>
