[HIGH] Rollback IDs are always undefined

After create_appointment or add_weight, code extracts ID via result.id || result.appointment_id. Backend success responses return {status: success, message: ...} with no id field. Rollback ID is always undefined, undo permanently broken.\n\nFile: Frontend/src/services/ActionExecutor.js, lines ~209 and ~335\nFix: Update backend add_* endpoints to return newly created row's ID.