Function run_create_file 

async fn run_create_file(
    client: &PasswordManagerClient,
    request: SendAddRequest,
    path: &str,
) -> Result<SendView>

Full file-send create pipeline:

1. Read the plaintext file bytes.
2. create_file_send encrypts them under the send key it derives, sends the ciphertext length as file_length, registers the send, and returns the encrypted bytes plus upload metadata (URL + backend).
3. The ciphertext is uploaded via upload_send_file, which dispatches to the Direct or Azure backend based on the file_upload_type from step 2.