Introduces distinct Dockerfiles for documentation and slide projects, enhancing modularity and build efficiency. The previous monolithic structure was less flexible and caused longer build times.
- Added `DOCMACHINE_DOCS_ENABLE` and `DOCMACHINE_SLIDES_ENABLE` env variables to toggle features.
- Created `docker/Dockerfile.docs` for documentation builds, including necessary tools and dependencies.
- Created `docker/Dockerfile.slides` for slide builds to streamline setup.
- Updated main Dockerfile to include `python-is-python3` for compatibility, removing redundant symlinks.
- Enhanced LaTeX tools by adding `texlive-xetex` and extra fonts for improved PDF output.
