Add option to persist session after claude code disconnects

[TristanFloch]

Summary

Add monet-persist-sessions option to keep sessions alive after Claude Code
disconnects, allowing reconnection without restarting the server.

Problem

Closes #33.

When Claude Code disconnects (e.g., exiting the CLI), the monet session is
automatically cleaned up. Users who frequently restart Claude Code sessions while
keeping Emacs running must manually restart the monet server each time before
reconnecting.

Solution

Add a new customizable variable monet-persist-sessions (default nil) that, when
enabled, keeps the websocket server running after Claude disconnects. The session
remains available for a new Claude Code session to reconnect via /ide.

Usage

(setq monet-persist-sessions t)

Test plan

I first set up my Doom Emacs configuration to use this option: link to the exact line.

While multiple monet servers are running on different directories:

• Start a monet server for a new project directory using monet-start-server
• Connect to that server using /ide in Claude Code (using a standalone terminal)
• Terminate the Claude Code session using Ctrl+C Ctrl+C
• Check the monet session is still running using monet-list-sessions:

  doom                 Port: 11617 Connected: No  Initialized: Yes  Directory: /Users/myuser/myproject/
  

• Restart Claude Code in the same directory using ENABLE_IDE_INTEGRATION=t claude and check it connected to the right session
• Double check the monet sessions list:

  doom                 Port: 11617 Connected: Yes Initialized: Yes  Directory: /Users/myuser/myproject/