feat: update ConnectionDropMenu 3D source to use generate3d

Change THREE_D_SOURCE_OPTIONS from nanoBanana to generate3d with
cube icon and "Generate 3D" label.

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

src/components/ConnectionDropMenu.tsx

@@ -321,11 +321,11 @@ const THREE_D_TARGET_OPTIONS: MenuOption[] = [
 // 3D source options (nodes that produce 3D output)
 const THREE_D_SOURCE_OPTIONS: MenuOption[] = [
   {
-    type: "nanoBanana",
-    label: "Generate Image",
+    type: "generate3d",
+    label: "Generate 3D",
     icon: (
       <svg className="w-4 h-4" fill="none" viewBox="0 0 24 24" stroke="currentColor" strokeWidth={1.5}>
-        <path strokeLinecap="round" strokeLinejoin="round" d="M2.25 15.75l5.159-5.159a2.25 2.25 0 013.182 0l5.159 5.159m-1.5-1.5l1.409-1.409a2.25 2.25 0 013.182 0l2.909 2.909m-18 3.75h16.5a1.5 1.5 0 001.5-1.5V6a1.5 1.5 0 00-1.5-1.5H3.75A1.5 1.5 0 002.25 6v12a1.5 1.5 0 001.5 1.5zm10.5-11.25h.008v.008h-.008V8.25zm.375 0a.375.375 0 11-.75 0 .375.375 0 01.75 0z" />
+        <path strokeLinecap="round" strokeLinejoin="round" d="M21 7.5l-2.25-1.313M21 7.5v2.25m0-2.25l-2.25 1.313M3 7.5l2.25-1.313M3 7.5l2.25 1.313M3 7.5v2.25m9 3l2.25-1.313M12 12.75l-2.25-1.313M12 12.75V15m0 6.75l2.25-1.313M12 21.75V19.5m0 2.25l-2.25-1.313m0-16.875L12 2.25l2.25 1.313M21 14.25v2.25l-2.25 1.313m-13.5 0L3 16.5v-2.25" />
       </svg>
     ),
   },