Add a new "retro" theme option that mimics the classic Windows 98 aesthetic, providing a nostalgic alternative to the modern and classic dark themes.
Changes include:
- Defining CSS variables for the retro theme in `00-base.css` (pixel fonts, silver/gray colors, and classic window shadows).
- Adding custom styling for cards, headers, buttons, and title bars to replicate classic OS windows.
- Adding a star background GIF (`stars1.gif`).
- Excluding the retro theme from modern "revamp" styles in `15-revamp.css`.
- Updating `CLAUDE.md` with instructions on screenshot verification.
- Update navigation labels from "My Account" to "Dashboard" and "Login" to "Sign in", updating tests accordingly.
- Redesign settings forms into structured sections with improved spacing and layout.
- Add CSS styles for tabs, small buttons, and responsive settings sections to enhance the user experience.
