I've done a fair number of NextAuth to Better Auth moves, and they're mostly mechanical: same general shape, swap the library, fix a few call sites. Clerk is a different animal, and you should know that going in. NextAuth is a library. Clerk is a hosted product: pre-built React components plus a hosted user store that lives on Clerk's servers. When you move off Clerk you're not swapping one auth library for another — you're replacing UI you never wrote, re-implementing session logic Clerk did...