refactor: introduce modern frontend

frontend/index.html

@@ -0,0 +1,16 @@
+<!DOCTYPE html>
+<html lang="">
+
+<head>
+  <meta charset="UTF-8">
+  <link rel="icon" href="/favicon.ico">
+  <meta name="viewport" content="width=device-width, initial-scale=1.0">
+  <title>coconut-leaf</title>
+</head>
+
+<body>
+  <div id="app"></div>
+  <script type="module" src="/src/main.ts"></script>
+</body>
+
+</html>