fix: add audio target handle to audioInput in getNodeHandles

AudioInputNode has both a target and source audio handle, but
getNodeHandles only declared the output. This prevented valid
connections from GenerateAudio's audio output to AudioInput's
audio input.

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

src/components/WorkflowCanvas.tsx

@@ -111,7 +111,7 @@ const getNodeHandles = (nodeType: string): { inputs: string[]; outputs: string[]
     case "imageInput":
       return { inputs: ["reference"], outputs: ["image"] };
     case "audioInput":
-      return { inputs: [], outputs: ["audio"] };
+      return { inputs: ["audio"], outputs: ["audio"] };
     case "annotation":
       return { inputs: ["image"], outputs: ["image"] };
     case "prompt":