Provider approval option for client self-scheduling

Add an optional setting that requires provider approval before a client appointment is officially scheduled, instead of automatic booking. Currently, when a client self-schedules, the appointment is automatically confirmed, which can create challenges if there is a scheduling conflict, a calendar error, or something the provider forgot to block off. The requested process:

• A client selects an available appointment time and submits a scheduling request.

• The provider receives a notification and can approve or decline the request.

• The requested time is temporarily held to prevent double-booking while awaiting approval.

• Once approved, the appointment is officially added to the calendar, and the client receives a confirmation.

• If declined, the client receives a notification encouraging them to select another time.

Providers should be able to choose between automatic booking and approval-required scheduling based on their preferences.