Extract independent MIT Mortar kit and contribution workflow

playground/index.html

@@ -0,0 +1,12 @@
+<!doctype html>
+<html lang="en">
+  <head>
+    <meta charset="UTF-8" />
+    <meta name="viewport" content="width=device-width,initial-scale=1" />
+    <title>Mortar component playground</title>
+  </head>
+  <body>
+    <div id="root"></div>
+    <script type="module" src="/main.tsx"></script>
+  </body>
+</html>