- Create LanguageSelector component with dropdown (shows flag + name)
- Add LanguageSelector to Header (right side, near user email/logout)
- Add LanguageSelector to login, signup, and signup/[code] pages
- Create test-utils.tsx with renderWithProviders helper
- Add vitest.setup.ts to mock localStorage
- Update all test files to use renderWithProviders
- Language selector persists choice in localStorage
- HTML lang attribute updates dynamically based on selected language
All frontend and e2e tests passing.