fix: use direct favicon.ico, open links in app mode (popup window)

- Favicon loaded directly from website's /favicon.ico instead of
  Google's service (which was unreliable/blocked on internal networks)
- Letter-initial fallback when favicon can't be loaded
- External links open in popup window (app mode) instead of new tab

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

packages/frontend/src/admin/AdminExternalLinksPage.tsx

@@ -7,11 +7,11 @@ function generateId(): string {
   return Date.now().toString(36) + Math.random().toString(36).slice(2, 10);
 }
 
-/** Favicon-URL aus einer Website-URL ableiten (Google Favicon Service) */
+/** Favicon-URL direkt von der Webseite laden */
 function getFaviconUrl(url: string): string | null {
   try {
-    const domain = new URL(url).hostname;
-    return `https://www.google.com/s2/favicons?domain=${domain}&sz=32`;
+    const parsed = new URL(url);
+    return `${parsed.origin}/favicon.ico`;
   } catch {
     return null;
   }

packages/frontend/src/shell/AppLayout.tsx

@@ -12,11 +12,11 @@ interface ExternalLink {
   sortOrder: number;
 }
 
-/** Favicon-URL aus einer Website-URL ableiten (Google Favicon Service) */
+/** Favicon-URL direkt von der Webseite laden */
 function getFaviconUrl(url: string): string | null {
   try {
-    const domain = new URL(url).hostname;
-    return `https://www.google.com/s2/favicons?domain=${domain}&sz=32`;
+    const parsed = new URL(url);
+    return `${parsed.origin}/favicon.ico`;
   } catch {
     return null;
   }
@@ -82,37 +82,52 @@ export function AppLayout() {
                   <a
                     key={link.id}
                     href={link.url}
-                    target="_blank"
-                    rel="noopener noreferrer"
+                    onClick={(e) => {
+                      e.preventDefault();
+                      window.open(
+                        link.url,
+                        link.label,
+                        'popup,noopener',
+                      );
+                    }}
                     className={styles.navLink}
                   >
-                    {favicon ? (
-                      <img
-                        src={favicon}
-                        alt=""
-                        style={{
-                          width: 16,
-                          height: 16,
-                          objectFit: 'contain',
-                          borderRadius: 2,
-                        }}
-                      />
-                    ) : (
-                      <svg
-                        width="16"
-                        height="16"
-                        viewBox="0 0 16 16"
-                        fill="none"
-                        stroke="currentColor"
-                        strokeWidth="1.5"
-                        strokeLinecap="round"
-                        strokeLinejoin="round"
-                      >
-                        <path d="M10 2h4v4" />
-                        <path d="M6 10L14 2" />
-                        <path d="M14 9v4a1 1 0 01-1 1H3a1 1 0 01-1-1V3a1 1 0 011-1h4" />
-                      </svg>
-                    )}
+                    <img
+                      src={favicon || ''}
+                      alt=""
+                      style={{
+                        width: 16,
+                        height: 16,
+                        objectFit: 'contain',
+                        borderRadius: 2,
+                      }}
+                      onError={(e) => {
+                        // Fallback: erstes Zeichen des Labels als Text-Icon
+                        const el = e.target as HTMLImageElement;
+                        el.style.display = 'none';
+                        const fallback = el.nextElementSibling;
+                        if (fallback)
+                          (fallback as HTMLElement).style.display =
+                            'flex';
+                      }}
+                    />
+                    <span
+                      style={{
+                        display: 'none',
+                        width: 16,
+                        height: 16,
+                        alignItems: 'center',
+                        justifyContent: 'center',
+                        fontSize: '0.625rem',
+                        fontWeight: 700,
+                        background: 'rgba(255,255,255,0.15)',
+                        borderRadius: 2,
+                        color: 'rgba(255,255,255,0.8)',
+                        flexShrink: 0,
+                      }}
+                    >
+                      {link.label.charAt(0).toUpperCase()}
+                    </span>
                     {link.label}
                     <svg
                       width="10"