Migrate away from Radix Theme

[pbruvoll]

When starting tekkendocs we used radix themes https://www.radix-ui.com/ which is a complete design system. After some experience, I would prefer just using the radix base components from https://www.radix-ui.com/primitives and use the design system from https://ui.shadcn.com/ which builds on these primitives.
We have already started using some components from shadcn. Button and Input are located in \tekkendocs@\components\ui\

[pbruvoll]

Currently, we are using Card, Badge, Text, Flex, Table, Heading, and Inset from Radix theme.
The migration might be implemented with several PRs.
For Text and Heading, we can just use plain tailwind classes.