feat: react quickstart app style update

[fcoppede]

updated the style, look and feel of the react quickstart app to match the idea we have for the SPA app:

1. New font
2. Match Zitadel colors for login/logout button
3. Add decoded JWT to the home page
4. Added more detailed instructions to the readme file
5. Updated the oidc client to the latest version

[mffap]

While trying out the example, I didn't follow the instructions exactly. So I ended up getting a bearer token, which didn't result in an error, just the start page again after a login.
I had to go to the console, but I also got only the information about a 400 status from the Zitadel response. Without any knowledge this would have been hard to debug.

Can we render error responses in the application?

[mffap]

I left some comments, overall the application works. I just had a couple of comments that might improve the DevX a bit more.

[fcoppede]

thanks @mffap just updated the code based on your comments. I cleaned up the readme file and fixed the app so it will not break if the token is not in JWT format.

[github-actions]

🎉 This PR is included in version 1.1.1 🎉

The release is available on:

• npm package (@latest dist-tag)
• GitHub release

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