feat: bootstrap MediaStationGo (Go + React rewrite of MediaStation)

Adopt the cropflre/nowen-video tech stack and rebuild the project from
scratch:

  - Backend: Go 1.25 + Gin + GORM + SQLite (WAL) + JWT + WebSocket hub.
    Layered packages config / database / model / repository / service /
    middleware / handler. Default admin (admin/admin123) seeded on first
    run; /api routes for auth, libraries, media, stream and admin
    panels. WebSocket scan-progress events at /api/ws.
  - Frontend: React 18 + Vite 5 + Tailwind 3.4 + Zustand + axios +
    react-router 6 + lucide-react + framer-motion + hls.js. Pages for
    Login / Home / Library / Search / MediaDetail / Player / Admin
    (Library, Users, Settings tabs).
  - Distribution: multi-arch Dockerfile (frontend -> backend -> Alpine
    runtime), docker-compose.yml, GitHub Actions for CI and GHCR
    publish, Makefile, env-prefixed config (MEDIASTATION_*).
  - Docs: README, CONTRIBUTING, .env.example, config.example.yaml.

Backend builds, vets and tests pass. Frontend builds via tsc -b && vite
build (250 kB JS / 16 kB CSS, gzipped 84 / 4 kB).

web/src/components/RequireAuth.tsx

@@ -0,0 +1,23 @@
+import { ReactNode } from 'react'
+import { Navigate, useLocation } from 'react-router-dom'
+
+import { useAuthStore } from '../stores/auth'
+
+// Route guard: redirects to /login when no token is present.
+export function RequireAuth({ children }: { children: ReactNode }) {
+  const token = useAuthStore((s) => s.token)
+  const location = useLocation()
+  if (!token) {
+    return <Navigate to="/login" replace state={{ from: location }} />
+  }
+  return <>{children}</>
+}
+
+// Route guard: only allows users with role === "admin".
+export function RequireAdmin({ children }: { children: ReactNode }) {
+  const user = useAuthStore((s) => s.user)
+  if (user?.role !== 'admin') {
+    return <Navigate to="/" replace />
+  }
+  return <>{children}</>
+}