pages: add Jekyll front matter to API ref so just-the-docs renders pages

Without front matter, Jekyll treats every generated .md as a static
file and copies it verbatim to _site/ instead of rendering it through
the just-the-docs layout. The api-reference URLs returned raw markdown
(or 404 when the user expected .html).

- Add docs/_api-frontmatter.tpl with title, default layout, and
  nav_exclude:true (the 3,979-page API surface would otherwise drown
  the sidebar; users reach pages via search and direct links).
- Pass --front-matter to xmldocmd in the pages workflow.

xmldocmd's $title placeholder is substituted per page; combined with
search_exclude:false the pages still get indexed by just-the-docs'
search.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: mariotoffia

.github/workflows/pages.yml

@@ -47,6 +47,7 @@ jobs:
           mkdir -p docs/api-reference
           xmldocmd /tmp/fd-publish/FluentDocker.dll docs/api-reference \
               --source https://github.com/mariotoffia/FluentDocker/tree/master/FluentDocker \
+              --front-matter docs/_api-frontmatter.tpl \
               --clean
 
       - name: Setup Ruby

docs/_api-frontmatter.tpl

@@ -0,0 +1,6 @@
+---
+title: $title
+layout: default
+nav_exclude: true
+search_exclude: false
+---