Small layout adjustments and form errors in partial outsourced

app/views/categories/index.html.erb

@@ -1,4 +1,16 @@
-<% content_for :title, "Kategorien & Typen" %>
+<% content_for :title, "Kategorien" %>
+
+<!-- NEU: Fügt den Hinzufügen-Button oben rechts in die Hauptleiste ein -->
+<% content_for :top_bar_actions do %>
+  <%= link_to new_category_path, class: "py-2 px-4 text-sm font-semibold rounded-lg bg-blue-600 text-white hover:bg-blue-700 flex items-center gap-1.5 shadow-sm transition" do %>
+    <svg class="h-4 w-4" fill="none" viewBox="0 0 24 24" stroke-width="2" stroke="currentColor">
+      <path stroke-linecap="round" stroke-linejoin="round" d="M12 4.5v15m7.5-7.5h-15" />
+    </svg>
+    <div class="hidden md:inline">
+      Kategorie anlegen
+    </div>
+  <% end %>
+<% end %>
 
 <div class="space-y-6">