fix(api): quote filename in Content-Disposition download header

The filename token was unquoted, producing a malformed header for any
video whose stem contains spaces or special characters. Per RFC 6266,
the filename parameter must be a quoted-string.

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

Author: Mihir7027

app/controllers/v1/video.py

@@ -495,7 +495,7 @@ async def download_video(request: Request, file_path: str):
     file_path = pathlib.Path(video_path)
     filename = file_path.stem
     extension = file_path.suffix
-    headers = {"Content-Disposition": f"attachment; filename={filename}{extension}"}
+    headers = {"Content-Disposition": f'attachment; filename="{filename}{extension}"'}
     return FileResponse(
         path=video_path,
         headers=headers,