[Rubyfi]

This pull request introduces a dual documentation build system, ensuring that documentation is generated and verified using both Sphinx and ubCode (ubc). It updates documentation, build scripts, configuration files, and adds a license. The main goal is to guarantee that both documentation builds have matching content, with automated checks in CI.

Dual documentation build and verification:

• Added a dual build process in the CI workflow (.github/workflows/pr_checks.yml) to generate documentation with both Sphinx and ubCode, and introduced a parity check to ensure both builds have the same content.
• Added new scripts: build_doc_ubc.sh for building docs with ubCode, and check_build_parity.py for verifying content parity between the two builds. Updated README.md to document these scripts and explain the dual build process. [1] [2]

ubCode-specific configuration and styling:

• Added docs/_static/ubc-custom.css to map brand colors and style variables for ubCode’s theme, ensuring visual consistency with the Sphinx (furo) theme.
• Updated docs/ubproject.toml to configure ubCode’s HTML builder, including theme, logo, CSS, repository links, and PlantUML integration to match Sphinx’s configuration. Also added custom link handling for source code references. [1] [2]

PlantUML update:

• Updated the PlantUML jar version in docs/conf.py and ubproject.toml to ensure compatibility with both Sphinx and ubCode builds. [1] [2]

Licensing:

• Added an MIT License file and referenced it in the README.md to clarify project licensing. [1] [2]