feat: 新增视频播放页面

- 新增 /video/:id 路由与 VideoPage 组件
- 视频文件通过 /uploads/videos/{id}.mp4 静态访问
- .gitignore 排除 videos 目录，避免大文件入库

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

packages/web/src/App.tsx

@@ -4,6 +4,7 @@ import LandingPage from "./pages/LandingPage";
 import AlbumPage from "./pages/AlbumPage";
 import ArticlePage from "./pages/ArticlePage";
 import MusicPage from "./pages/MusicPage";
+import VideoPage from "./pages/VideoPage";
 import AdminLogin from "./admin/AdminLogin";
 import AdminGuard from "./admin/AdminGuard";
 import AdminLayout from "./admin/AdminLayout";
@@ -29,6 +30,7 @@ export default function App() {
         <Route path="/collect/:stampId" element={<CollectRedirect />} />
         <Route path="/article/:id" element={<ArticlePage />} />
         <Route path="/music/:id" element={<MusicPage />} />
+        <Route path="/video/:id" element={<VideoPage />} />
 
         {/* Admin panel */}
         <Route path="/admin" element={<AdminLogin />} />