[Change Requests] - Buffer-days input in Admin tools

Description

Context
Admins need to see and change the activation buffer (a number of days stored on the organization as activationBufferDays) from Admin Tools → Project Configuration. The backend endpoint that saves the value is handled separately; this ticket is the api call, hook, and the input itself.

Task
should show the number and an edit button have a modal pop up for editing the buffer window

Acceptance Criteria

• A frontend api function and a react-query hook call the update endpoint for activationBufferDays.
• The Project Configuration tab shows the current buffer value in a labeled number input.
• An admin can change the value and save it; after saving, the input reflects the saved value.
• The input doesn't let you submit a negative or non-integer value (matches the backend rule).

Start in the Project Configuration tab and trace its existing data flow to identify the frontend API functions and react-query hooks used there. Add the activationBufferDays update call, labeled editable number input, modal and save behavior; done means saved values reappear and negative or non-integer submissions are rejected.