feat: multi-pane split view for side-by-side buffer comparison

[mpryor]

Summary

Allow viewing two or more buffers simultaneously in split panes (horizontal or vertical) within the same screen.

Details

• Split the view horizontally or vertically to display multiple buffers at once
• Each pane operates independently (scroll, filter, search)
• Keybinding to toggle split, switch focus between panes, and close panes
• Optionally sync scroll position between panes for line-by-line comparison

Use Cases

• Compare filtered vs unfiltered data side by side
• Monitor two log streams simultaneously
• View raw and parsed versions of the same data
• Compare before/after a transformation

Considerations

• Keybinding design — vi-style ctrl+w window management
• Textual framework layout capabilities for dynamic pane splitting
• Minimum pane size constraints on small terminals
• Whether to support more than two panes