refactor: split send function into smaller helper functions

- Extract prepare_endpoint() for endpoint configuration
- Extract prepare_temp_directory() for temp directory creation
- Extract validate_share_path() for path validation
- Extract setup_data_sharing() for data sharing setup
- Extract create_send_result() for result creation
- Replace complex progress logic with ProviderProgressTracker
- Improve code maintainability and readability

Author: bruceblink