refactor: extract helper functions from handle_environment_creation

- Extract load_configuration() helper for config loading/validation
- Extract execute_create_command() helper for command execution
- Extract display_creation_results() helper for result display
- Main function reduced from ~58 to 21 lines (orchestration only)
- Add comprehensive unit tests for each helper function
- All existing tests pass without behavioral changes

Co-authored-by: josecelano <58816+josecelano@users.noreply.github.com>

Author: Copilot