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/head/css.html

@@ -0,0 +1,19 @@
+{{- with resources.Get "css/main.css" }}
+  {{- if hugo.IsDevelopment }}
+    <link rel="stylesheet" href="{{ .RelPermalink }}">
+  {{- else }}
+    {{- with . | minify | fingerprint }}
+      <link rel="stylesheet" href="{{ .RelPermalink }}" integrity="{{ .Data.Integrity }}" crossorigin="anonymous">
+    {{- end }}
+  {{- end }}
+{{- end }}
+
+{{- with resources.Get "css/custom.css" }}
+  {{- if hugo.IsDevelopment }}
+    <link rel="stylesheet" href="{{ .RelPermalink }}">
+  {{- else }}
+    {{- with . | minify | fingerprint }}
+      <link rel="stylesheet" href="{{ .RelPermalink }}" integrity="{{ .Data.Integrity }}" crossorigin="anonymous">
+    {{- end }}
+  {{- end }}
+{{- end }}