feat: frontend improvements — UI polish, player bar, auth flow, i18n
- Header, Sidebar, Toast, Dropdown, EmptyState component refinements
- Auth flow: LoginPage, RegisterPage, AuthInput, AuthLayout improvements
- Player bar: glass effect, progress, track info, controls enhancements
- Dashboard, Discover, Search pages updates
- PlaylistCard, TrackCard component improvements
- Auth store and API interceptors hardening
- i18n: updated en/es/fr locale files
- CSS additions in index.css
- Package.json and vite config updates
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
4b57b46bac