feat: Tab-Navigation als Hamburger-Menü

3-Striche-Button öffnet Dropdown mit allen Kategorien.
Aktive Kategorie wird neben dem Button angezeigt.
Klick außerhalb schließt das Menü.

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

js/app.js

@@ -15,6 +15,18 @@ export const state = {
   }
 };
 
+// Hamburger-Menü
+const menuToggle = document.getElementById('menu-toggle');
+const menuDropdown = document.getElementById('menu-dropdown');
+const menuActiveLabel = document.getElementById('menu-active-label');
+
+menuToggle.addEventListener('click', (e) => {
+  e.stopPropagation();
+  menuDropdown.classList.toggle('open');
+});
+
+document.addEventListener('click', () => menuDropdown.classList.remove('open'));
+
 // Tab-Navigation
 document.querySelectorAll('.tab-btn').forEach(btn => {
   btn.addEventListener('click', () => {
@@ -24,6 +36,8 @@ document.querySelectorAll('.tab-btn').forEach(btn => {
     btn.classList.add('active');
     const section = document.getElementById('tab-' + tab);
     if (section) section.classList.add('active');
+    menuActiveLabel.textContent = btn.textContent;
+    menuDropdown.classList.remove('open');
   });
 });