Require `@` for user profile view at the beginning in URL

Currently, when I visit the URL:

https://explore.openhive.network/@blocktrades - correctly shows me the blocktrades profile, but when I enter the URL:

https://explore.openhive.network/blocktrades - redirects me to the locktrades profile.

This can leave space for bad actors who may want to impersonate other profiles, such as well-known exchanges, popular witnesses etc.

The expected behavior is to return a 404 page, when the path does not match any existing paths or @ at the beginning, as hiveblocks.com now acts.