Push all docs/ content to GitHub Pages (MkDocs build + deploy)

[RedjiJB]

Deploy the full 14-document docs/ set to GitHub Pages via MkDocs.\n1. Create mkdocs.yml at repo root with nav structure matching the numbered docs\n2. Add docs/ as MkDocs source directory\n3. Add .github/workflows/docs.yml — triggered on push to main, runs mkdocs gh-deploy\n4. Enable GitHub Pages on it-stack-docs repo (source: gh-pages branch)\n5. Verify live at https://it-stack-dev.github.io/it-stack-docs/