feat(dashboard): add Content Engine concept and dashboard link

dashboard/index.html

@@ -153,6 +153,16 @@
             <a href="/gtm/" class="btn">Starten &rarr;</a>
         </div>
 
+        <!-- Content Engine -->
+        <div class="card">
+            <span class="card-icon">✍️</span>
+            <h2>Content Engine</h2>
+            <p>
+                The "Mouth" for your Strategy. Generiert SEO-Websites, LinkedIn-Posts und Mail-Sequenzen aus GTM-Daten.
+            </p>
+            <a href="/content/" class="btn">Starten &rarr;</a>
+        </div>
+
         <!-- Company Explorer (Robotics) -->
         <div class="card">
             <span class="card-icon">🤖</span>