Replace localStorage workflow with res.cookies workflow

[kamarmack]

const unsubscribe = auth.onAuthStateChanged((user) => {
  setUser(() => user);
  return void (async () => {
    try {
      if (user) {
        const idToken = await user.getIdToken();
        localStorage.setItem("firebase_auth_jwt", idToken);
      } else {
        localStorage.removeItem("firebase_auth_jwt");
      }
    } catch (err) {
      console.error(err);
      localStorage.removeItem("firebase_auth_jwt");
    }
  })();
});