Eighth admin page. Documents the hidden-by-default create form (and why:
admin creation stays available with registration disabled — the form's
own design comment), live password requirements from active settings,
the card controls with their guards (last admin cannot be demoted or
deleted, dropdowns/buttons disable themselves with explanations), the
admin Edit User Profile modal (profile fields + role + Change Password
without current password — the admin-only difference), and delete
semantics (account + everything owned: devices, sessions, reading
data). Closes the loop on roles: admins get the Administration section;
users see only libraries visible to them, linking libraries.md for the
visibility story. Glossary gains + Create User and Edit User Profile.
(Settings referenced in prose only until that page lands — the first
amend of this commit briefly carried the same forward-link mistake the
dashboard page's amend fixed; pipefail is now the rule.)
