refactor templates layout

@see https://gohugo.io/templates/new-templatesystem-overview/

layouts/_partials/header/site-header.html

@@ -0,0 +1,64 @@
+<header class="site-header h-card">
+  {{ block "header" . }}
+    <h2
+      class="p-name site-header__title"
+      itemprop="name"
+    >
+      <a
+        class="u-url"
+        href="{{ .Site.Home.RelPermalink }}"
+        rel="me author"
+        >{{ .Site.Title }}</a
+      >
+    </h2>
+    <p
+      class="p-note site-header__tagline"
+      itemprop="about"
+    >
+      Views my own. Discussion ≠ endorsement. Do try this at home.
+    </p>
+    <p class="site-header__icons">
+      ~
+      <a
+        class="u-email"
+        aria-label="Email"
+        href="mailto:{{ $.Site.Params.adminEmail }}"
+        rel="me"
+        >✉️</a
+      >
+      ~
+      <a
+        class="u-url"
+        aria-label="Code Forge"
+        href="{{ .Site.Params.codeURL }}"
+        rel="me"
+        >🧑‍💻</a
+      >
+      ~
+      <a
+        class="u-key"
+        aria-label="PGP key"
+        href="/{{ .Site.Params.keyfile }}"
+        rel="me"
+        >&#128272;</a
+      >
+      ~
+      <a
+        href="/index.xml"
+        aria-label="{{ .Site.Title }} RSS feed"
+        ><img
+          class="feed-icon"
+          alt="RSS feed"
+          src="{{ .Site.Params.feedIcon }}"
+      /></a>
+      ~
+    </p>
+    <nav class="site-header__nav">
+      <ul>
+        {{ range ( where .Site.Sections.ByTitle "Type" "in" site.Params.mainSections ) }}
+          <li><a href="{{ .RelPermalink }}">{{ .Title | safeHTML }}</a></li>
+        {{ end }}
+      </ul>
+    </nav>
+  {{ end }}
+</header>