Migrate to Vite

Create React App is no longer maintained. The last non-patch release is by now older than 2 years, aeons in web development. There are various pain points with Create React App, for example the long start up times and the high memory usage during bundling, which sometimes caused pipelines to fail. Mantine also does not officially support C-R-A anymore starting with version 7.0.

Thus, I migrated to the new kid on the block: Vite. The start up time and builds are now significantly faster and Vite is officially supported by Mantine (and also recognized as the go-to option by many other libraries).

I've opted to use the old eslint configuration (eslint-config-react-app) for now. Eventually we should improve upon that, since parts of that config are no longer maintained either and there are by now many more advanced rules in e.g. @typescript-eslint:recommended-type-checked.

Finally, I decided to split our deps into dependencies and devDependencies. This only has an impact if one calls yarn install --production, which we don't do in our CI. However I hope this separation makes it a bit easier for newer developers to understand which packages are relevant at which point in the process.