fix: preserve panel background in cursor mode (renderTextCursorContent)

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.

vcom.toml

@@ -4,7 +4,7 @@ right_path = ''
 
 [ui]
 app_title = 'vcom'
-theme = 'catppuccin-mocha'
+theme = 'nord-frost'
 icon_mode = 'auto'
 show_title_bar = true
 show_footer = true