Tidy up dependencies

[pfw13]

1. Currently, the root level package.json has some dependencies. In most cases, in a monorepo, the root shouldn't have any dependencies. Rather, they should be moved to the individual app / library that depends on them. In our case, all the dependencies in the root package.json seem to belong into apps/react/package.json. This can be done by adding the --filter flag to the respective pnpm command, e.g., pnpm add @emotion/styled --filter react
2. It seems that we use multiple libraries for the same purpose. E.g., "react-icons" was added as a root level dependence, although we already had "@heroicons/react" installed for that case. We should tidy this up and agree on one library per purpose.