Ad-hoc screening endpoints!

We've added a new ah-hoc screening end point to support use-cases where you just want to send a new question and document context on the fly (rather than from a pre-made template) and receive an AI suggested answer directly using:POST /workspaces/{workspace_id}/adhoc-screenings

https://briink.readme.io/reference/create_adhoc_screening_workspaces__workspace_id__adhoc_screenings_post

We also added API documentation for this new ah-hoc screening endpoints with clearer descriptions and usage guidance.