fix(remote): forward collaboration mode and handle disconnect

[slkzgm]

Part of the optional remote backend RFC (#54).

Summary

This is a small follow-up on top of #121 to make remote mode behave the same as local mode for collaboration selection, and to avoid commands hanging indefinitely after a daemon restart / TCP disconnect.

Changes

• Forward collaborationMode in remote send_user_message.
• Proxy collaboration_mode_list in remote mode.
• Make the remote client fail fast after disconnects:
  • Track a shared connected flag
  • Drain pending requests when the read loop ends or the write loop hits an IO error

Notes

• Default behavior remains unchanged (only active when backendMode=remote).

Validation

• npm run lint
• npm run typecheck
• npm run build