Migrate from mkdocs-material to zensical

[nanxstats]

This PR migrates the documentation site generator framework from mkdocs-material to zensical.

Also migrated the GitHub Actions workflow, did some cleanup.

[Copilot]

Pull request overview

This PR migrates the documentation site generator from mkdocs-material to zensical, a newer documentation framework. The migration includes updating configuration files, dependencies, and build scripts.

Key changes:

• Replaced mkdocs.yml with zensical.toml configuration
• Updated dependencies in pyproject.toml and uv.lock to use zensical instead of mkdocs-material
• Modified build scripts to use zensical commands
• Added test fixture RTF output files

Reviewed changes

Copilot reviewed 25 out of 63 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
zensical.toml	New configuration file for zensical documentation framework with project settings, navigation, theme, and plugin configurations
uv.lock	Removed mkdocs-material and related dependencies (babel, backrefs, certifi, charset-normalizer, idna, requests, urllib3, mkdocs-material-extensions, paginate); added zensical and deepmerge
pyproject.toml	Updated dev dependencies to replace mkdocs and mkdocs-material with zensical>=0.0.15
mkdocs.yml	Deleted old mkdocs configuration file
scripts/check_rtf.sh	Updated to use zensical build command instead of mkdocs build
docs/scripts/sync.sh	Updated comment to reference Zensical instead of mkdocs
tests/fixtures/docs_outputs/*.rtf	Added multiple test fixture RTF files for documentation validation

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.