Simplify Sidebar: Remove Woerterbuch, rename to "Lernmodule"

Sidebar: Only "Lernmodule" link (no separate Woerterbuch).
/learn page: "Neue Lernunit erstellen" button links to /vocabulary
for the word selection flow. Teacher stays in one flow.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

studio-v2/app/learn/page.tsx

@@ -101,6 +101,7 @@ export default function LearnPage() {
   const [units, setUnits] = useState<LearningUnit[]>([])
   const [isLoading, setIsLoading] = useState(true)
   const [error, setError] = useState<string | null>(null)
+  const [showCreate, setShowCreate] = useState(false)
 
   const glassCard = isDark
     ? 'bg-white/10 backdrop-blur-xl border border-white/10'
@@ -209,6 +210,25 @@ export default function LearnPage() {
           </div>
         )}
 
+        {/* Create new unit button */}
+        {!isLoading && (
+          <div className="mb-4">
+            <a
+              href="/vocabulary"
+              className={`inline-flex items-center gap-2 px-5 py-3 rounded-xl font-medium transition-all ${
+                isDark
+                  ? 'bg-gradient-to-r from-blue-500 to-cyan-500 text-white hover:shadow-lg hover:shadow-blue-500/25'
+                  : 'bg-gradient-to-r from-blue-500 to-cyan-500 text-white hover:shadow-lg'
+              }`}
+            >
+              <svg className="w-5 h-5" fill="none" stroke="currentColor" viewBox="0 0 24 24">
+                <path strokeLinecap="round" strokeLinejoin="round" strokeWidth={2} d="M12 4v16m8-8H4" />
+              </svg>
+              Neue Lernunit erstellen
+            </a>
+          </div>
+        )}
+
         {!isLoading && units.length > 0 && (
           <div className="grid gap-4">
             {units.map(unit => (