Admin Create Asclepius Invite

Mint + send a personal Asclepius (physician-evaluator) onboarding link on behalf of a named lead (internal admin only). Unlike /health-systems/invite above (which mints a generic, unpersonalized link for the clinical/TEAM product), this locks the invite to product="asclepius" and ties it to one email, reusing the exact minting + cap logic the public self-serve endpoint uses (routers.onboarding.self_serve_invite) so an admin-sent invite and a physician-typed-their-own-email invite share one counter and one shape.