Prepares a batch for finalization by fully recalculating it, checking that it does not contain validation errors, and setting a temporary StatusId of 35, "Being finalized". For draft batches the recalculation is offloaded to the queue: this route responds with the error "BatchOperationOffloaded", and the finalization GUID is delivered over SignalR (PrepareFinalizeSalaryBatchSuccess) once the batch is ready. The GUID can also be read from the batch itself via GET once StatusId is 35. For already approved batches no recalculation is needed and the GUID is returned directly in the response. The "Being finalized" status will automatically revert after 30 minutes if the batch has not been finalized in the meantime. The function requires the permission salarybatch.canfinalize