feat: update files for Hono router and SPA support

frontend/public/index.html

@@ -1,6 +1,7 @@
 <!doctype html>
 <html lang="ja">
   <head>
+    <base href="/" />
     <meta charset="UTF-8" />
     <meta name="viewport" content="width=device-width, initial-scale=1.0" />
     <title>ポッドキャスト管理画面</title>