Reserve important routes like `/login` from Merchant Registration

Once logged in, looks like you signup a merchant `/login`.

May want to reserve some common slugs from registration: `/about` , `/logout` etc...

Start by tracing merchant registration and how submitted slugs are validated; the issue does not name specific files or tests. Confirm which application routes must be protected, including /login, /about, and /logout. Done means reserved paths cannot be registered as merchants while those routes remain reachable.

Written by the indexing model from the issue text.