fix: update Mantine example / cleanup layout

[aheissenberger]

• add AppShell
• fix Navigation

open tasks - need help:

• [ ] Navigation / How to get the current path from the router to show the active item in the navigation

[lazarv]

Thanks @aheissenberger for the changes on the example, this looks a lot nicer now!

What I did on your branch:

• cleaned up getConfig exports, these are not used by the framework
• used usePathname to get the current pathname to enable displaying the active link
• fixed navigation progress, there was a missing CSS import in the layout
• fixed logo and title styling

The only change that might need some clarification is the pathname usage. When rendering the menu on the server-side there was no active link as usePathname imported from @lazarv/react-server/navigation module is a client only hook. But when hydrating the app, it provides the proper pathname on the client causing a hydration error. So I used the server-side equivalent of usePathname from the core module and passed it down to the MainNavigation component. There could be some enhancement on the frameworks part to transfer some server-side data to client-side hooks when rendering client components on the server-side.