Assign Google Business Profile location to another profile

Connect a Google Business Profile location onto a DIFFERENT profile by reusing the OAuth grant from an already-connected Google Business Profile account, with no browser and no re-authorization. Built for agencies whose single Google account has manager access to many client locations and who run one profile per client: connect one location the normal way (browser OAuth), then bulk-assign the rest onto each client's profile via this endpoint. The path accountId is a SOURCE connected Google Business Profile account (the token holder); the body profileId is the TARGET profile. Returns 409 if the target profile already has a Google Business Profile connection (switch its location with PUT gmb-locations instead).