Fix: Move 'import os' to top-level to prevent NameError at startup

main.py

@@ -1,4 +1,5 @@
 from fastapi import FastAPI, UploadFile, File, Depends, HTTPException, Header, Form
+import os
 from fastapi.staticfiles import StaticFiles
 from fastapi.responses import FileResponse
 from auth import verify_api_key
@@ -40,7 +41,6 @@ async def detect_voice(
     audio_url: str = Form(None),
     x_api_key: str = Depends(verify_api_key)
 ):
-    import os
     UPLOAD_DIR = os.path.join(os.getcwd(), "uploads")
     os.makedirs(UPLOAD_DIR, exist_ok=True)