init: scaffold OPENBUREAU site with shibui-derived theme

- Hugo site for openbureau.ch (Deutsch, i18n-ready for EN/IT)
- Theme themes/openbureau/ = local copy of shibui, customized via
  site-level layouts and assets to keep the theme reference clean
- Editorial typography stack: Newsreader serif body, Space Grotesk
  display, Inter for listings, IBM Plex Mono for technical meta
- Content structure: library/ (Theorie, Büroführung, Software) with
  manifest and colophon at root; software is a library category, not
  a separate top-level
- Three views over one source: Journal (chronological home),
  Library (atlas grouped by section + tag cloud), single articles

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

layouts/_default/single.html

@@ -0,0 +1,41 @@
+{{ define "main" }}
+  {{ partial "terms.html" (dict "taxonomy" "tags" "page" .) }}
+
+  <article class="single">
+    <header class="single-header">
+      <h1>{{ .Title }}</h1>
+      {{ with .Params.summary }}
+        <p class="single-summary text-muted">{{ . }}</p>
+      {{ end }}
+    </header>
+
+    {{/* Table of Contents */}}
+    {{ $hasToC := .Params.toc | default true }}
+    {{ $headers := findRE "<h[2-6]" .Content }}
+    {{ if and $hasToC (ge (len $headers) 1) }}
+      <nav class="toc">
+        <strong>Inhalt</strong>
+        <div class="toc-content">{{ .TableOfContents }}</div>
+      </nav>
+    {{ end }}
+
+    <div class="single-content">
+      {{ .Content }}
+    </div>
+
+    <div class="time">
+      {{ partial "date.html" .Date }}
+      {{ $showReadingTime := .Params.showreadingtime | default site.Params.showreadingtime | default true }}
+      {{ if and $showReadingTime .ReadingTime }}
+        <span class="reading-time"> · {{ .ReadingTime }} min Lesezeit</span>
+      {{ end }}
+      {{ $showLastMod := .Params.showlastmod | default site.Params.showlastmod | default false }}
+      {{ if and $showLastMod .Lastmod }}
+        {{ if ne (.Lastmod.Format "2006-01-02") (.Date.Format "2006-01-02") }}
+          <span class="lastmod"> · Zuletzt aktualisiert: {{ .Lastmod.Format "2006-01-02" }}</span>
+        {{ end }}
+      {{ end }}
+    </div>
+  </article>
+
+{{ end }}