Add .gitattributes to enforce LF line endings for shell scripts

[pergyz]

This pull request introduces improvements to Docker client handling for better platform compatibility, adds SSL support to the ui command, and ensures consistent line endings for shell scripts. Below are the most significant changes:

Docker client handling improvements:

• Added a new get_docker_client function in src/magentic_ui/_docker.py to handle platform-specific Docker client initialization, particularly for Windows environments.
• Replaced direct calls to docker.from_env() with get_docker_client() across multiple functions, including check_docker_running, build_browser_image, build_python_image, check_browser_image, and check_python_image. This ensures consistent Docker client initialization. [1] [2] [3] [4]

SSL support for ui command:

• Added ssl_certfile and ssl_keyfile parameters to the ui command in src/magentic_ui/backend/cli.py, enabling optional SSL configuration. [1] [2]
• Updated the uvicorn.run call to conditionally include SSL certificate and key file paths if provided, ensuring secure HTTPS support. [1] [2]

Miscellaneous:

• Updated .gitattributes to enforce LF line endings for all .sh files, ensuring consistent behavior across platforms.This pull request includes a small change to the .gitattributes file. The change ensures that all .sh files will have line endings normalized to LF (eol=lf).