feat: status buffer

[d12frosted]

Summary

Emacs buffer showing publicatorg server status and build progress.

Display

*publicatorg: <project>* buffer showing:

• Server state (running/stopped)
• Current build status (idle/building/error)
• Recent build log (last N builds with times)
• Current errors (if any)
• Queued changes (if watching)

Interactive

• Button/key to force rebuild
• Button/key to stop/start server
• Click error to jump to source

Priority

After server mode (#7) works. Start with message output, add buffer later.

Dependencies

• feat: server mode with incremental builds #7 (server mode)