- Add automatic JSON and XML formatting for response bodies
- Replace TextView with GtkSourceView for syntax highlighting
- Add syntax selector dropdown (RAW/JSON/XML) for request body
- Use Source Code Pro font (12pt) for better readability
- Integrate with GNOME theme (Adwaita light/dark)
- Add line numbers and current line highlighting
- Persist syntax selection when saving/loading requests
- Maintain backward compatibility with existing saved requests