feat: server mode with incremental builds

[d12frosted]

Summary

Transform publicatorg from run-once batch tool to long-running server with incremental builds.

Watch Mode

• Monitor file system for changes (filenotify, or receive explicit signals)
• Debounce rapid changes
• Trigger incremental rebuild

Incremental Intelligence

• Track dependencies at output level (not just note level)
• Rebuild only affected outputs
• Handle transitive dependencies (note A links to B; B changes; A's output may need rebuild)

Status Reporting

• What's currently building
• Build times per output
• Error collection and display
• Progress indication for large builds

Control Interface

• Start/stop server
• Force full rebuild
• Pause/resume watching
• Query build status

State Machine

idle → watching → building → idle

Open Questions

• In-Emacs or separate process?
• How to handle builds that take longer than change frequency?
• External trigger support (git hooks, manual command)?