Replace full ANSI reset sequences (\x1b[0m) added by lipgloss.Render() for
gutter markers, cursor highlights, and selection highlights with
background-preserving resets (\x1b[39;22;23;24;59;48;2;R;G;Bm) that restore
the panel background color.
Without this fix, every \x1b[0m from lipgloss-styled elements in
renderTextCursorContent resets the panel background (set by the outer
renderPreviewContent wrapper), causing some letters to have incorrect or
missing background color in caret mode.
