Add Neat Annotations support to generated example pages

[Copilot]

This adds annotation callouts to example pages using the Neat Annotations library, with annotation content configured per example slug and rendered by the site generator. The change introduces a new attachment pipeline parallel to figures so callouts can be managed centrally without editing source examples.

• Annotation asset integration

  • Added Resources/neat-annotations.css to the project and output copy list.
  • Wired generated pages to load the local annotation stylesheet and the Shantell Sans font used by annotation labels.

• Slug-based annotation mapping

  • Added Marginalia/AnnotationAttachments.cs with a registry of per-example annotation definitions (Text, Note, direction/color classes, optional context).
  • Added retrieval API returning normalized CSS class payloads for rendering.

• Generation pipeline wiring

  • Updated Nocco.GenerateHtml to resolve annotations by slug and pass them into Webpage.razor.
  • Updated Nocco.GenerateAsync to emit neat-annotations.css into the generated site.

• Template + styling updates

  • Extended Webpage.razor parameters with PathToAnnotationsCss and ExampleAnnotations.
  • Added an annotation banner section that renders callouts between figure banners and runner output.
  • Added banner/layout styles in Resources/nocco.css for readable callout grouping.

• Docs + coverage

  • Added Neat Annotations links to docs/README.md.
  • Added unit coverage for annotation attachment lookup in NoccoTests.

// Nocco.cs
var slug = new DirectoryInfo(source).Name;
var exampleAnnotations = AnnotationAttachments.GetAnnotations(slug).ToList();

var dictionary = new Dictionary<string, object?>
{
    { "PathToAnnotationsCss", Path.Combine(pathToRoot, "neat-annotations.css").Replace('\\', '/') },
    { "ExampleAnnotations", exampleAnnotations },
};