Add option to kill buffer on Claude exit

[remo5000]

Summary

• Adds claude-code-kill-buffer-on-exit defcustom (default nil)
• When non-nil, automatically kills the Claude buffer when the process exits (e.g., via /quit)
• Adds process sentinel to handle the cleanup

Credit

This PR is based on work by @titaniumbones from stevemolitor/claude-code.el#114. Rebased onto current main.

Original PR description

I am more comfortable keeping focus in the claude-code buffer, and so I end up quitting via /quit. This feature kills the buffer when the process dies. Pretty sure this feature would be useful to others?

• new defcustom claude-code-kill-buffer-on-exit; when non-nil, kill claude buffer when quitting manually with /quit
• new sentinel claude-code--process-sentinel that performs kill if appropriate.

🤖 Generated with Claude Code

[remo5000]

@titaniumbones I hope you don't mind -- I wanted to use this feature so I'm merging into my fork. Thank you for authoring it!