Make large "+ new task" FAB use text gold

Make the prominent "+ new task" floating action button match the primary
text gold color in the Onyx theme. The FAB previously used the cream
primary color; this change sets its background to #d4bc72 so the button
visually aligns with other gold text elements in the UI.

apps/tauri/src/app.css

@@ -171,6 +171,11 @@ body {
   color: #141414;
 }
 
+/* FAB: match text gold instead of cream primary */
+[data-theme="onyx"] .rounded-full.bg-primary.shadow-lg {
+  background-color: #d4bc72;
+}
+
 /* Checkbox borders: gold instead of gray */
 [data-theme="onyx"] .border-gray-400,
 [data-theme="onyx"] .border-gray-500 {