fix: wrap WAV Buffer in Uint8Array for NextResponse compatibility

NextResponse's BodyInit type doesn't accept Node.js Buffer directly.
Wrapping in Uint8Array satisfies the type and works at runtime.

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

app/api/generate/route.ts

@@ -74,7 +74,7 @@ export async function GET(req: NextRequest) {
 
   const filename = `${safeName}_click.wav`;
 
-  return new NextResponse(wav, {
+  return new NextResponse(new Uint8Array(wav), {
     status: 200,
     headers: {
       "Content-Type": "audio/wav",