Removes a document association row by document_associations.association_id for the authenticated tenant. The service deletes rows where association_id and tenant match and does not verify entity_type in this method. The controller intends to return an empty success response after deletion, but currently calls createApiResponse(null, 204) inside NextResponse.json, which can throw because JSON responses cannot use status 204 with a body. In the current route wiring, req.context may also be absent because no route-level API-key auth wrapper sets it, causing a 500 before deletion.