fix(tui): preserve list prefixes in copy mode

[shaheislam]

Summary

Fixes TUI copy mode so yanking rendered lines preserves list/status prefixes that are visible in the UI.

This covers both:

• Markdown source prefixes like - item, 1. item, and - [x] item
• Separate same-row rendered prefixes like [✓] Inspect current branch

Before

After

Details

Copy mode previously copied the main rendered text for a row but could drop prefixes when they were rendered separately or
transformed from Markdown source.

This change tracks horizontal renderable positions so copy mode can include visible same-row prefixes to the left of the
copied content. It also restores Markdown list markers from the original source where available, so rendered bullets or task
checkboxes copy back as Markdown.

Tests

• Added focused copy-mode regression tests for Markdown list prefixes
• Added focused copy-mode regression tests for visible same-row prefixes
• Ran bun test test/cli/tui/vim-motions.test.ts
• Ran bun typecheck

[shaheislam]

@leohenon Hi Leo I've raised a small QoL fix for markdown highlighting in visual mode if you wouldn't mind taking a look please

[leohenon]

good fix, thanks!