fix: add z-index to OutputNode handles so they paint above content

The content div's `relative` positioning creates a stacking context that
paints over the handles. Adding zIndex: 10 matches the pattern used by
GenerateImageNode and GenerateVideoNode.

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

src/components/nodes/OutputNode.tsx

@@ -120,13 +120,14 @@ export function OutputNode({ id, data, selected }: NodeProps<OutputNodeType>) {
           position={Position.Left}
           id="image"
           data-handletype="image"
+          style={{ zIndex: 10 }}
         />
         <Handle
           type="target"
           position={Position.Left}
           id="audio"
           data-handletype="audio"
-          style={{ top: "60%", background: "rgb(167, 139, 250)" }}
+          style={{ top: "60%", background: "rgb(167, 139, 250)", zIndex: 10 }}
         />
 
         {contentSrc ? (