Mark a clinician-invited parent at claim time - server twin of appweb markInvitedParent's direct Supabase write. Endpoint only for now: no client calls it yet.

Family invites never need this: their accept route runs the same transition inline with FAMILY_PARENT. Best-effort like every post-claim transition - by the time the client calls this the claim is committed, so a refused flip is reported (profile_updated=false), never raised. Claim refresh stays client-side, as above.