[bug fix] Fix auto grouping doesn't work because isOn is undefined by default

[jt-wang]

Theres' a bug that auto grouping doesn't work.

This is because in background.ts, it executes auto grouping only when Chrome local storage isOn is true.

const enable = await getStorage<boolean>("isOn");
  if (
    !enable ||
    !tab.id ||
    !tab.url ||
    window.type != "normal" ||
    !types.length ||
    (tab.status === "complete" && tab.url.startsWith("chrome://"))
  ) {
    return;
  }

However, isOn is by default undefined, because popup.tsx doesn't store isOn value to Chrome local storage, as the only place it sets is when user clicks on disableGrouping.

  const disableGrouping = () => {
    setIsOn((isOn) => {
      setStorage("isOn", !isOn);
      return !isOn;
    });
  };

Since isOn is undefined, backtround.ts won't execute auto grouping.

This PR fixes this.

---

48 is aimed to avoid such bugs when these states should have been synced across browser storage and React states.

[jt-wang]

@MichaelYuhe Great suggestion! updated.