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/pages/PlayerPage.tsx

@@ -0,0 +1,53 @@
+import { useEffect, useRef, useState } from 'react'
+import { useNavigate, useParams } from 'react-router-dom'
+import { ArrowLeft } from 'lucide-react'
+
+import { mediaAPI } from '../api/library'
+import { streamURL } from '../api/client'
+import type { Media } from '../types'
+
+// Fullscreen, dark-themed video page. We currently use direct play via
+// /api/stream/:id — the future task is wiring HLS.js for transcoded streams.
+export function PlayerPage() {
+  const { id = '' } = useParams()
+  const navigate = useNavigate()
+  const ref = useRef<HTMLVideoElement>(null)
+  const [media, setMedia] = useState<Media | null>(null)
+
+  useEffect(() => {
+    if (!id) return
+    mediaAPI.get(id).then(setMedia)
+  }, [id])
+
+  useEffect(() => {
+    const onKey = (e: KeyboardEvent) => {
+      if (e.key === 'Escape') navigate(-1)
+    }
+    window.addEventListener('keydown', onKey)
+    return () => window.removeEventListener('keydown', onKey)
+  }, [navigate])
+
+  return (
+    <div className="-m-6 flex min-h-screen flex-col bg-black md:-m-8">
+      <button
+        onClick={() => navigate(-1)}
+        className="absolute left-4 top-4 z-10 flex items-center gap-2 rounded-full bg-black/60 px-3 py-1.5 text-sm text-white backdrop-blur transition hover:bg-black/80"
+      >
+        <ArrowLeft size={16} /> 返回
+      </button>
+      <div className="flex flex-1 items-center justify-center">
+        {media ? (
+          <video
+            ref={ref}
+            src={streamURL(media.id)}
+            controls
+            autoPlay
+            className="max-h-screen w-full max-w-[1600px] bg-black"
+          />
+        ) : (
+          <p className="text-slate-500">加载中…</p>
+        )}
+      </div>
+    </div>
+  )
+}