feat(ui): redesign login panel with modern glassmorphism style

- Add animated gradient background with floating blobs
- Use glassmorphism card with backdrop blur
- Add brand logo with theme-aware switching (light/dark)
- Improve form layout with input icons and better spacing
- Make login button full-width for better UX
- Add loading state for login button
- Improve passkey button styling with dashed border
- Respect prefers-reduced-motion for animations

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: EstrellaXD