Create a separate route for category edit page

The category page /category/:slug can be in two vastly different states: the main public page, and the metadata edit page.

Having both of them be on the same URL is bad UX, so I have separated the edit page into a /category/:slug/edit subpage using a local Route component. I've also made it so it will redirect to the main category page if you're unauthorised.

All the logic (editing category name (which changes url), cancel, save, etc) is still confirmed to be working.