Sicherheitscheck: Schwachstellen behoben

- Pfad-Traversal: safeFilename/containedPath-Helper, storeAnhang sanitizes
  filename, alle Download/Delete/Mail-Send-Routen pruefen Containment
- Stored XSS: serveInline entscheidet Viewable-Typ nur nach Extension,
  nicht nach client/seitigem MIME; nicht viewbare Typen werden als Download
  erzwungen. Upload fileFilter (Basis/Interne) + Extension-Validierung
  (Signatur/Foto leiten Ext aus MIME, blockieren .html)
- URL-Scheme-Allowlist (safeUrl) fuer quelle_url-hrefs gegen javascript:-XSS
- E-Mail-Iframe: Sandbox auf allow-same-only (kein allow-popups-to-escape)
- Sicherheits-Header: CSP, X-Content-Type-Options, X-Frame-Options,
  Referrer-Policy, COOP; x-powered-by aus; jsPDF self-hosted unter /vendor
- Session: Secure-Flag bei TLS, serverseitige absoluteexpiry, Scrypt async
  + Dummy-Verify gegen Timing/Enumerate + Login-Rate-Limit
- Open Redirect: /email/fetch nur same-origin Redirects
- SSRF: Validierung von OLLAMA_HOST/CALDAV_URL/MAIL_HOST gegen
  Metadata/Link-Local-BLock (localhost/LAN bleibt erlaubt)
- Globaler Error-Handler ohne Interna-Leak, env=production

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

public/js/chat.js

@@ -24,13 +24,21 @@
   }
 
   // Minimal markdown → HTML. HTML is escaped first, so model output can never
-  // inject markup; only the markdown tokens below are turned into tags.
+  // inject markup; only the markdown tokens below are turned into tags. Link
+  // targets are restricted to http(s)/mailto/relative so a `javascript:` URL
+  // from the model cannot become a clickable XSS vector, and the URL is stripped
+  // of characters that could break out of the href attribute.
   function inlineFmt(t) {
     return t
       .replace(/`([^`]+)`/g, '<code>$1</code>')
       .replace(/\*\*([^*]+)\*\*/g, '<strong>$1</strong>')
       .replace(/(^|[^*])\*([^*]+)\*/g, '$1<em>$2</em>')
-      .replace(/\[([^\]]+)\]\(([^)\s]+)\)/g, '<a href="$2" target="_blank" rel="noopener">$1</a>');
+      .replace(/\[([^\]]+)\]\(([^)\s]+)\)/g, (m, label, url) => {
+        const u = String(url).trim();
+        if (u && !/^(https?:|mailto:|\/|#)/i.test(u)) return m;
+        const safe = u.replace(/["'<>`\\]/g, '');
+        return `<a href="${safe}" target="_blank" rel="noopener noreferrer">${label}</a>`;
+      });
   }
 
   function renderMarkdown(src) {