Move Jekyll site from _build/ to docs/

Add Jekyll frontmatter (title, layout, nav_order, parent) to all docs/ files so they serve both the Jekyll site and the TypeScript lib. Remove _build/ directory entirely. Update _config.yml, index.md links, CI workflow, and help.ts web URLs.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: chrismo

.github/workflows/pages.yml

@@ -40,7 +40,7 @@ jobs:
       - name: Generate version info
         run: |
           mkdir -p _data
-          LAST_UPDATED=$(git log -1 --format=%cs -- _build/)
+          LAST_UPDATED=$(git log -1 --format=%cs -- docs/)
           echo "# Auto-generated by CI build — do not edit manually" > _data/versions.yml
           echo "last_updated: \"${LAST_UPDATED}\"" >> _data/versions.yml