docs: publish MkDocs documentation site

[codeforester]

Summary

• Add a MkDocs Material site with navigation across the existing documentation set.
• Add strict docs builds and repository link/example validation to CI.
• Publish the reviewed site to GitHub Pages from main.
• Add the canonical Documentation project URL to package metadata and replace README/security docs links with PyPI-safe rendered-site links.
• Verify the Documentation URL in wheel metadata during artifact validation.

Issue

Closes #108

Validation

• bash tests/validate.sh
• python scripts/validate_docs.py
• python -m mkdocs build --strict --site-dir /private/tmp/base-cli-docs-site
• python -m pytest -q
• ruff check lib/python scripts examples tests compatibility
• Built and validated wheel/sdist metadata, including the Documentation project URL.

Deployment note

Repository Pages settings must use the GitHub Actions source and the github-pages environment must be approved for the first deployment.