Add initial JSON data files and implement core page components for game functionality

app/ViewModel/usePrivateGameViewModel.js

@@ -0,0 +1,31 @@
+import { useState } from 'react';
+import { joinPrivateGame } from '../API/API';
+import { getSession, setSessionGroup } from '../Model/SessionStore';
+
+const usePrivateGameViewModel = () => {
+  const [joinCode, setJoinCode] = useState('');
+  const [error, setError] = useState('');
+
+  const joinWithCode = async () => {
+    setError('');
+    try {
+      const { currentUid } = getSession();
+      const group = await joinPrivateGame({ userId: currentUid, joinCode: joinCode.trim().toUpperCase() });
+      setSessionGroup(group.Gid);
+      return group;
+    } catch (e) {
+      setError(e.message);
+      return null;
+    }
+  };
+
+  return {
+    joinCode,
+    error,
+    setJoinCode,
+    joinWithCode,
+  };
+};
+
+export default usePrivateGameViewModel;
+