A client-side app is any app where the code is executed on the clients side, so for example if a website is making API requests in that page itself, then that’s client-side as the requests are being made from whichever user is viewing that page. Because the requests are made from the user in a client-side app, no private information, such as a client secret, or any OAuth token other than one from the user themselves, can be used.
Circumventing the 3rd party Twitch API and scraping the Twitch site itself could be a violation of the Twitch Developer Agreement. I’d strongly recommend against it.