- Add .ce-card class with shadow and rounded corners to match native ChatGPT popup
- Remove Tailwind border/rounded/shadow from menu popup in favor of .ce-card
- Strengthen --ce-border-light fallbacks for visible menu item borders
- Fix Select dropdown: auto width with right padding for arrow clearance
- Add ._export variant for export dialog background
Closes#357
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>