AIXE endpoint: /aixe/clients/list-available-service-times
Discovery request: GET /aixe/clients/list-available-service-times/?
Action request: POST /aixe/clients/list-available-service-times

Purpose:
Lists valid requested start times for a cleaning and date.

Required fields:
ClientKey, InvoiceKey, RequestedDate in YYYY-MM-DD format.

Optional fields:
None.

Rules:
Availability reflects operating hours and estimated cleaning duration; it is not an official reservation.

Response convention:
SuccessCode is SUCCESS when the operation completes. Success is true on success. Errors return SuccessCode ERROR, Success false, and a Message. Numeric database IDs are never returned.