ui: Zitieren zeigt Quellenangabe sichtbar + Copy-Fallback für HTTP

Vorher: stiller clipboard.writeText → tut auf HTTP/LAN nichts (Clipboard-API
nur in sicherem Kontext). Jetzt: Klick klappt ein Panel mit der lesbaren
Quellenangabe auf (user-select:all), „Kopieren" nutzt clipboard-API mit
execCommand-Fallback; schlägt das fehl, wird der Text markiert (manuelles
Strg/⌘+C).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

layouts/_partials/provenance.html

@@ -12,26 +12,67 @@
       <span class="prov-sep">·</span>
     {{ end }}
   {{ end }}
-  <button type="button" class="prov-cite"
+  <button type="button" class="prov-cite" aria-expanded="false"
     data-title="{{ .Title }}"
     data-author="{{ $author }}"
     data-url="{{ .Permalink }}"
     {{ with .GitInfo }}data-version="{{ .AbbreviatedHash }}"{{ end }}>Zitieren</button>
 </div>
+<div class="prov-citation" hidden>
+  <p class="prov-citation-text"></p>
+  <div class="prov-citation-actions">
+    <button type="button" class="prov-citation-copy">Kopieren</button>
+    <span class="prov-citation-status" role="status"></span>
+  </div>
+</div>
 <script>
   (function () {
     if (window.__provCite) return; window.__provCite = 1;
-    document.querySelectorAll('.prov-cite').forEach(function (btn) {
-      btn.addEventListener('click', function () {
-        var d = btn.dataset;
-        var today = new Date().toLocaleDateString('de-CH');
-        var v = d.version ? ', Version ' + d.version : '';
-        var cite = d.author + ': ' + d.title + '. OPENBUREAU' + v + '. Abgerufen am ' + today + ', ' + d.url;
-        navigator.clipboard.writeText(cite).then(function () {
-          var t = btn.textContent; btn.textContent = 'Kopiert ✓';
-          setTimeout(function () { btn.textContent = t; }, 1500);
-        }).catch(function () {});
+    var btn = document.querySelector('.prov-cite');
+    var panel = document.querySelector('.prov-citation');
+    if (!btn || !panel) return;
+    var textEl = panel.querySelector('.prov-citation-text');
+    var copyBtn = panel.querySelector('.prov-citation-copy');
+    var statusEl = panel.querySelector('.prov-citation-status');
+
+    var d = btn.dataset;
+    var today = new Date().toLocaleDateString('de-CH');
+    var v = d.version ? ', Version ' + d.version : '';
+    // Format: Autor: Titel. OPENBUREAU, Version xxx. Abgerufen am TT.MM.JJJJ, URL
+    var cite = d.author + ': ' + d.title + '. OPENBUREAU' + v + '. Abgerufen am ' + today + ', ' + d.url;
+    textEl.textContent = cite;
+
+    function selectText() {
+      var r = document.createRange(); r.selectNodeContents(textEl);
+      var sel = window.getSelection(); sel.removeAllRanges(); sel.addRange(r);
+    }
+    function copy() {
+      if (navigator.clipboard && navigator.clipboard.writeText) {
+        return navigator.clipboard.writeText(cite);
+      }
+      // Fallback für unsichere Kontexte (HTTP/LAN): execCommand auf Auswahl.
+      return new Promise(function (resolve, reject) {
+        try {
+          var ta = document.createElement('textarea');
+          ta.value = cite; ta.style.position = 'fixed'; ta.style.opacity = '0';
+          document.body.appendChild(ta); ta.focus(); ta.select();
+          var ok = document.execCommand('copy');
+          document.body.removeChild(ta);
+          ok ? resolve() : reject();
+        } catch (e) { reject(e); }
       });
+    }
+
+    btn.addEventListener('click', function () {
+      var open = panel.hasAttribute('hidden');
+      if (open) { panel.removeAttribute('hidden'); selectText(); }
+      else { panel.setAttribute('hidden', ''); }
+      btn.setAttribute('aria-expanded', String(open));
+    });
+    copyBtn.addEventListener('click', function () {
+      copy().then(function () { statusEl.textContent = 'Kopiert ✓'; })
+            .catch(function () { statusEl.textContent = 'Markiert — bitte mit Strg/⌘+C kopieren.'; selectText(); });
+      setTimeout(function () { statusEl.textContent = ''; }, 3000);
     });
   })();
 </script>