feat: Serve frontend build and static files, and fix server routing

frontend/public/index.html

@@ -1,12 +1,12 @@
-<!DOCTYPE html>
+<!doctype html>
 <html lang="ja">
-<head>
-  <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>
-</head>
-<body>
-  <div id="root"></div>
-  <script type="module" src="../src/index.tsx"></script>
-</body>
+  <head>
+    <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>
+  </head>
+  <body>
+    <div id="root"></div>
+    <script type="module" src="../build/index.js"></script>
+  </body>
 </html>