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/layouts/list.html

@@ -1,14 +1,11 @@
-{{ define "header" }}
-  <header>
-    <hgroup>
-      <h1>{{ .Title }}</h1>
-      {{ with .Description }}<p>{{ . }}</p>{{ end }}
-    </hgroup>
-  </header>
-{{ end }}
-
 {{ define "content" }}
-  <main>
+  <article>
+    <header>
+      <h1>{{ .Title }}</h1>
+      {{- with .Description }}
+      <p>{{ . }}</p>
+      {{- end }}
+    </header>
     {{ .Content }}
-  </main>
+  </article>
 {{ end }}