Ensure new accounts / renames cannot use duo- or ai- prefixes

Problem

As outlined in Referencing Agents and Flows in the UI MVP Pro... (#580550) we not only need to make sure that Flows and Agents use @ai- or @duo- prefixes but also provide a baseline of assurance that others cannot pretend to be one these accounts.

Desired Outcome

Ban both new accounts from using ai- or duo- prefix as well as any rename from applying these prefixes.

Implementation Plan

TBD