update extension popup UI to match web app style
Changed color scheme from purple/indigo to purple/cyan/orange:
- Header: gradient from yellow-400 → orange-500 → pink-600 (firefly banner)
- Background: purple-50 → white → cyan-50 gradient
- Primary button: orange-600 with hover state
- Secondary button: purple-800 border
- Progress bar: orange → pink gradient
- Links and accents: orange-600
Matches web app's tailwind.config.js color system.