Sidebar links ignore <base href> on sites served from a sub-path #40

Summary

Sidebar links are rendered root-relative (href="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/docs/introduction"). A root-relative URL ignores <base href>, so a site exported with shelldocs build --base-href /my-repo/ and served from https://user.github.io/my-repo/ links to https://user.github.io/docs/introduction, which is a 404.

Steps to reproduce

1. shelldocs build --base-href /my-repo/ --output publish
2. Serve publish/ under /my-repo/ (for example GitHub Pages for a project repo).
3. Click any sidebar link.

Expected: /my-repo/docs/introduction.
Actual: /docs/introduction (404).

Where

• src/ShellDocs.Components/Chrome/DocsSidebarNode.razor (href="@Node.Url", href="@_index.Url")
• Probably the same for breadcrumbs, prev/next, the TOC's page links, package and version selectors and search results. Worth checking every place that renders a NavigationNode.Url.

Suggested fix

Render navigation links base-relative (docs/introduction, no leading slash) so they resolve against <base href>, or prefix them with NavigationManager.BaseUri's path. Add a test that renders the layout and asserts no chrome link starts with /, and check a --base-href export in a browser.