[Shewart]

Moves the docs site from ShellDocs 0.1.17-alpha to 0.1.19-alpha. Version bumps only; no site code changes were needed.

What the site gets:

• Table of contents works again (0.1.19): the site runs InteractiveServer, where the "On this page" highlight stopped following the scroll and TOC clicks went to the home page. The last section is now highlighted at the bottom of a page.
• Folder titles (0.1.18): the sidebar reads "MAUI (preview)" and "Avalonia (preview)" instead of "Maui" / "Avalonia".
• Border utilities in previews no longer lose to the base border colour, and llms.txt lists each group once.

Changes:

• docs/ShellIcons.Docs/ShellIcons.Docs.csproj: the four ShellDocs packages → 0.1.19-alpha
• README.md: version lines
• .github/workflows/docs.yml: ShellDocs.CLI 0.1.7-alpha → 0.1.19-alpha

Checked:

• ShellIcons.slnx Release build: 0 warnings
• All 18 docs pages, /llms.txt and /llms-full.txt return 200; /docs/nope returns 404
• In a browser (InteractiveServer): a TOC click scrolls to its heading, keeps the page path in the URL and moves the highlight; at the bottom the last section is highlighted
• shelldocs build with CLI 0.1.19 writes 18 pages, 404.html, search, 24 llms files and the sitemap

After merging, rebuild and push the docs image for the zuluville server.