POL-124: Migrate frontend from React Native to Next.js web app

- Replace mobile/ (Expo) with web/ (Next.js 16 + Tailwind + shadcn/ui)
- Pages: login, register, pending, championships, championship detail, registrations, profile, admin
- Logic/view separated: hooks/ for data, components/ for UI, pages compose both
- Types in src/types/ (one interface per file)
- Auth: Zustand store + localStorage tokens + cookie presence flag for proxy
- API layer: axios client with JWT auto-refresh

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

web/public/vercel.svg

@@ -0,0 +1 @@
+<svg fill="none" xmlns="http://www.w3.org/2000/svg" viewBox="0 0 1155 1000"><path d="m577.3 0 577.4 1000H0z" fill="#fff"/></svg>