feat: add native-rendered Electron app

[lihebi]

There are two ways to make the electron app:

• [Approach 1, server-based, preferred]: Host UI at localhost:3000 and API servers at localhost:4000, and use Electron window as a browser. This approach makes it possible to open the app in the browser, so that

  • users can access the browser extensions.
  • lightweight, no need to render another embedded Chromium (the Electron renderer)
  • This approach should also make it easy to re-use the server-app logic.

• [Approach 2, native-rendered]: Let host only API server on localhost:4000, and render the UI pages & components directly in Electron API. This is the regular way of using Electron.

This PR implements approach 2. It can now render the page without a problem. However, approach 1 should be the way to go. ~Therefore, this PR is only for reference.~

[lihebi]

this PR is only for reference.

Actually, this PR is a general platform to build approach 1 as well. I'm merging this.