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/_default/_markup/render-image.html

@@ -0,0 +1,20 @@
+{{- $alt := .Text -}} {{- $src := .Destination -}} {{- $title := .Title -}}
+
+<figure>
+  <img
+    src="{{ $src }}"
+    alt="{{ $alt }}"
+    loading="lazy"
+    {{
+    with
+    $title
+    }}
+    title="{{ . }}"
+    {{
+    end
+    }}
+  />
+  {{- with $alt }}
+  <figcaption>{{ . }}</figcaption>
+  {{ end -}}
+</figure>