Create Placement Note

Create a note on a placement, attributed to the API key's user.

Placement notes carry NoteType.PLACEMENT_SHARED_NOTE — the broker-team outreach-context type the web app and AI recommendations also write (it is not shared with the borrower or lender). Internal placement notes are never created or exposed here. Note: the placement description field (PATCH /placements/<id>) also appends a shared note on change; these endpoints are the canonical way to manage a placement's note collection.