feat: 重构页面、路由与业务组件，新增课程演示

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/pages/index.ts

@@ -1,2 +1,4 @@
-export { About } from "./About";
-export { Home } from "./Home";
+export { default as About } from "./About";
+export { default as Components } from "./Components";
+export { default as CourseDemo } from "./CourseDemo";
+export { default as Home } from "./Home";