Each venue controls instructor names on its own schedule

Venue admins can now choose the name an instructor uses on that venue's
schedule. The setting is clearly labelled as a venue schedule name and shows
how the current venue formats instructor names when no custom name is set.

This also works safely for instructors who collaborate across venues. Changing
their role or schedule name affects only the current venue; it does not replace
the professional's name or other profile details elsewhere. A save is shown as
successful only after the requested venue changes were actually stored.