hub: generic home page (not owned by any user) + admin-managed branding
The hub home page was the oldest site (a user's PrutFolio). Now it is a
generic page: title/tagline/intro come from global settings (hub_title/
hub_tagline/hub_intro), editable in Admin -> Settings (hub only). The roster
now shows ALL users (including the admin's own PrutFolio under /user/<slug>)
— no site is singled out as "the company" any more.
POST /admin/settings only updates tenancy when the field is present (a
separate branding form no longer accidentally flips the mode).
Co-Authored-By: Claude <noreply@…>
![(please configure the [header_logo] section in trac.ini)](/chrome/site/your_project_logo.png){kind=logo}
