Retrieve the path of the latest PSV PDF for a workflow

Returns the storage path of the most recently generated Provider Summary Verification (PSV) PDF for the credentialing workflow identified by id, without triggering a new generation. Use POST /credentialing-workflows/{id}/generate-psv to generate a new PSV. Returns 200 with {workflowId, psvPdfPath} when a completed PSV PDF is available. Returns 202 with {workflowId, status: "GENERATING"} when a PSV generation is currently in progress for the latest status transition — poll this endpoint again after a delay. Returns 404 when no PSV PDF has ever been generated for this workflow; call generate-psv to create one.