auth: read-only view accounts (view everything, modify nothing)
New users.readonly column + readonly in the session. Global guard in server.js
blocks every state-modifying method (POST/PUT/PATCH/DELETE) for read-only
accounts -> no comments, saves, settings, nothing. GET remains free, so they
can view everything (including admin panels). Sticky "read-only demo" banner in
the shell when such an account is logged in.
Co-Authored-By: Claude <noreply@…>