Add tag pages

Tag posts in frontmatter with tags: [go, networking]. Then one template makes a page for every tag in use, tags/[tag].jsx:

params(() => [...new Set(pages("articles/**").flatMap(p => p.tags ?? []))].map(tag => ({ tag })));
data({ title: `Tagged “${page.params.tag}”` });
<>
  <h1>{page.title}</h1>
  <ul>
    {pages({ path: "articles/**", where: { tags: page.params.tag } }).reverse().map(p =>
      <li><a href={p.path}>{p.title}</a></li>
    )}
  </ul>
</>

A tag index, tags/index.jsx, lists the generated pages, since page bodies run after every page exists:

data({ title: "Tags" });
<ul>{pages("tags").map(t => <li><a href={t.path}>{t.slug}</a></li>)}</ul>

Link each post's tags from the post layout:

{page.tags?.map(t => <a class="tag" href={`/tags/${t}`}>{t}</a>)}

To give one tag a hand-written page, add tags/go.md; it replaces the generated /tags/go and every other tag keeps its generated page. See Generated pages.