feat: ShellDocs 0.1.17 with llms.txt for AI agents

The site moves to a Docker image; the static export is no longer deployed.

The Dockerfile publishes the site into the ASP.NET runtime image. The workflow builds it on every pull request, checks that pages, search and llms.txt answer, and on a push to main pushes docker.zuluville.com/shelldocs-docs as :latest and :<short commit>. Login uses the REGISTRY_USERNAME and REGISTRY_PASSWORD secrets.

README gets a Deploying section; the deployment guide no longer says this site is on GitHub Pages. The Pages workflow stays there as an example.

The four packages and the version strings in the content and README. The home page's terminal replay shows graphite, the theme shelldocs init picks by default since 0.1.18.

ShellDocs 0.1.18 adds seven palettes (o.Theme, init --theme). The theming page gets a Colour presets section with a live demo: wwwroot/demos/presets.html loads tokens.css in an IframePreview and switches presets, since a preset recolours the whole document it is on. The 'Theme has no effect' text goes from theming, configuration and init; the tokens and CLI package pages mention the presets. The site stays on Graphite.

New CLI page for shelldocs preview, linked from build, deployment, the quick start and the CLI package page. The build and deployment pages say --base-href now puts the subpath in front of root-relative links.

Since 0.1.18 HTML entities in component attribute values are decoded, so the inline-tags page, the Card page and the agent rules no longer say they stay literal. The search page says SearchState, SidebarCollapseState and MobileNavState are gone.

docs: ShellDocs 0.1.18 (colour presets, shelldocs preview)

0.1.19 fixes the table of contents on interactive sites: the highlight follows the scroll again and clicking an entry stays on the page instead of going home. Also lists each llms.txt group once and points the page menu's chat links at SiteUrl.

chore: bump ShellDocs to 0.1.19-alpha