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>

themes/openbureau/layouts/_partials/menu.html

@@ -0,0 +1,51 @@
+{{- /*
+Renders a menu for the given menu ID.
+
+@context {page} page The current page.
+@context {string} menuID The menu ID.
+
+@example: {{ partial "menu.html" (dict "menuID" "main" "page" .) }}
+*/}}
+
+{{- $page := .page }}
+{{- $menuID := .menuID }}
+
+{{- with index site.Menus $menuID }}
+  <nav aria-label="Main navigation">
+    <ul>
+      {{- partial "inline/menu/walk.html" (dict "page" $page "menuEntries" .) }}
+    </ul>
+  </nav>
+{{- end }}
+
+{{- define "_partials/inline/menu/walk.html" }}
+  {{- $page := .page }}
+  {{- range .menuEntries }}
+    {{- $attrs := dict "href" .URL }}
+    {{- if $page.IsMenuCurrent .Menu . }}
+      {{- $attrs = merge $attrs (dict "class" "active" "aria-current" "page") }}
+    {{- else if $page.HasMenuCurrent .Menu .}}
+      {{- $attrs = merge $attrs (dict "class" "ancestor" "aria-current" "true") }}
+    {{- end }}
+    {{- $name := .Name }}
+    {{- with .Identifier }}
+      {{- with T . }}
+        {{- $name = . }}
+      {{- end }}
+    {{- end }}
+    <li>
+      <a
+        {{- range $k, $v := $attrs }}
+          {{- with $v }}
+            {{- printf " %s=%q" $k $v | safeHTMLAttr }}
+          {{- end }}
+        {{- end -}}
+      >{{ $name }}</a>
+      {{- with .Children }}
+        <ul>
+          {{- partial "inline/menu/walk.html" (dict "page" $page "menuEntries" .) }}
+        </ul>
+      {{- end }}
+    </li>
+  {{- end }}
+{{- end }}