EmailDetail: Links immer im neuen Tab öffnen

Nach DOMPurify-Sanitize alle <a>-Elemente auf target="_blank" +
rel="noopener noreferrer" setzen. Letzteres verhindert
window.opener-Tab-Hijacking. Sanitize + DOM-Walk in useMemo, läuft
nur bei Wechsel der Email neu.

frontend/src/components/email/EmailDetail.tsx

@@ -1,4 +1,4 @@
-import { useState, useEffect } from 'react';
+import { useState, useEffect, useMemo } from 'react';
 import { Reply, Forward, RotateCcw, Star, Paperclip, Link2, X, Download, ExternalLink, Trash2, Undo2, Save, FileDown } from 'lucide-react';
 import DOMPurify from 'dompurify';
 import { CachedEmail, cachedEmailApi } from '../../services/api';
@@ -52,6 +52,24 @@ export default function EmailDetail({
     setLocalStarred(email.isStarred);
   }, [email.id, email.isStarred]);
 
+  // Email-Body sanitizen + alle <a>-Links auf neuen Tab umstellen.
+  // rel="noopener noreferrer" verhindert window.opener-Tab-Hijacking.
+  const safeHtmlBody = useMemo(() => {
+    if (!email.htmlBody) return '';
+    const sanitized = DOMPurify.sanitize(email.htmlBody, {
+      FORBID_TAGS: ['script', 'style', 'iframe', 'object', 'embed', 'form'],
+      FORBID_ATTR: ['onerror', 'onload', 'onclick', 'onmouseover', 'onfocus'],
+      ADD_ATTR: ['target'],
+    });
+    const wrapper = document.createElement('div');
+    wrapper.innerHTML = sanitized;
+    wrapper.querySelectorAll('a').forEach((a) => {
+      a.setAttribute('target', '_blank');
+      a.setAttribute('rel', 'noopener noreferrer');
+    });
+    return wrapper.innerHTML;
+  }, [email.htmlBody]);
+
   const toggleStarMutation = useMutation({
     mutationFn: () => cachedEmailApi.toggleStar(email.id),
     onMutate: () => {
@@ -411,16 +429,7 @@ export default function EmailDetail({
         {showHtml && email.htmlBody ? (
           <div
             className="prose prose-sm max-w-none"
-            dangerouslySetInnerHTML={{
-              __html: DOMPurify.sanitize(email.htmlBody, {
-                // Scripte, Inline-Handler, Form-Elemente, externe Referenzen verbieten.
-                // Bilder + Links mit target=_blank bleiben zugelassen.
-                FORBID_TAGS: ['script', 'style', 'iframe', 'object', 'embed', 'form'],
-                FORBID_ATTR: ['onerror', 'onload', 'onclick', 'onmouseover', 'onfocus'],
-                // Links in neuen Tabs öffnen (verhindert window.opener-Angriffe)
-                ADD_ATTR: ['target'],
-              }),
-            }}
+            dangerouslySetInnerHTML={{ __html: safeHtmlBody }}
           />
         ) : (
           <pre className="whitespace-pre-wrap text-sm text-gray-700 font-sans">