refactor: standardize all Hugo templates — consistent landmark structure

All templates now follow: body > nav > article > header + content + footer

Removed:
- <hgroup> (redundant, header+h1+p serves same purpose)
- <main> (article is the content landmark)
- role="main" on article (incorrect ARIA)
- header block in baseof (header now inside article)

Standardized: default, docs, essay, notes, console, page, list, index.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

site/layouts/docs/single.html

@@ -1,16 +1,3 @@
-{{ define "header" }}
-  <header>
-    {{- if .Description -}}
-    <hgroup>
-      <h1>{{ .Title }}</h1>
-      <p>{{ .Description }}</p>
-    </hgroup>
-    {{- else -}}
-    <h1>{{ .Title }}</h1>
-    {{- end }}
-  </header>
-{{ end }}
-
 {{ define "content" }}
   <section data-layout="docs">
 
@@ -32,20 +19,25 @@
     </nav>
 
     <article>
+      <header>
+        <h1>{{ .Title }}</h1>
+        {{- with .Description }}
+        <p>{{ . }}</p>
+        {{- end }}
+      </header>
+
       {{ .Content }}
 
       {{- if or .PrevInSection .NextInSection -}}
-      <footer data-role="prev-next">
+      <footer>
         {{- with .NextInSection -}}
         <a href="{{ .RelPermalink }}" rel="prev">
-          <span aria-hidden="true">←</span> Previous
-          <span>{{ .LinkTitle }}</span>
+          <span aria-hidden="true">←</span> {{ .LinkTitle }}
         </a>
         {{- end -}}
         {{- with .PrevInSection -}}
         <a href="{{ .RelPermalink }}" rel="next">
-          Next <span aria-hidden="true">→</span>
-          <span>{{ .LinkTitle }}</span>
+          {{ .LinkTitle }} <span aria-hidden="true">→</span>
         </a>
         {{- end -}}
       </footer>