createAppointment only checked the caller held an allowed role, then booked
onto whatever doctor_uuid the request named — a doctor could book onto any
other doctor's calendar, a clinic onto doctors outside it, a secretary outside
their scope. Add canBookForDoctor(): doctor→own only, clinic→member doctors,
secretary→active scope + appointments.create permission, admin→any.
Regression: tests/Appointment/BookingScopeTest.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
