Agent panel thread is interrupted/terminated when closing the local Zed client on a remote SSH session, instead of continuing server-side

[Shaik-Sirajuddin]

When connected to a remote host via Zed's SSH remote development, closing
the local Zed client (or losing the connection) sends an interrupt/stop
signal to any active Agent Panel thread, instead of letting it continue
running on the remote daemon.

Zed's remote architecture already keeps the project/language-server daemon
alive across disconnects (proxy mode reconnects transparently), and
terminals sent via ClientMessage::Detach are meant to keep running
server-side rather than being killed (per discussion #50584). Agent panel
threads don't get the same treatment: closing the client mid-run
interrupts the thread rather than detaching it, so long-running agent
tasks can't survive a client disconnect/reconnect cycle.

This is related to but distinct from:

• SSH Remote Projects: queued agent messages lost across disconnect/reconnect #57252 (queued messages lost across disconnect/reconnect)
• Remote development project and remote terminal agent sessions disconnect frequently #59394 (remote agent sessions disconnect frequently)
• RFC: Persistent terminal sessions across Zed restarts #50584 (RFC for persistent terminal sessions)

Expected behavior: an active Agent Panel thread should detach and keep
running on the remote daemon when the local client closes/disconnects,
the same way terminal sessions are intended to, and reattach to the
in-progress thread on reconnect.

Actual behavior: the thread receives a user-interrupted signal and
stops when the client/SSH connection closes.

Environment: Zed connected to a remote host over SSH remote development.