Complete shadcn/ui migration: remove all CSS modules, establish design system
- Delete all 4 CSS module files (common, collect, topnavbar, secondarynav)
- Add brand/accent/signal color tokens to tailwind.config.js
- Update Button default variant to use brand teal instead of blue
- Add shadcn Select and Badge ui primitives; install @radix-ui/react-select
- Migrate all 20 components to shadcn Card, DropdownMenu, Button, Badge
- Replace nav CSS class string props with typed status/active props
- All 25 tests pass, clean build
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
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