Api responses better error handling

When I gave a wrong index name, I got this error

provide a proper resposne by putting this in a error object

```
{
"error":{
"detail": "Error in faiss::FileIOReader::FileIOReader(const char *) at /Users/runner/work/faiss-wheels/faiss-
wheels/faiss/faiss/impl/io.cpp:68: Error: 'f' failed: could not open data/flutter/index.faiss for reading: No such file or directory"
}
}
```

Start by locating the API endpoint that handles an invalid index name and inspect how the FAISS file-opening error currently reaches the response. Done means that this failure returns the requested error object with the detail message instead of the shown raw error.

Written by the indexing model from the issue text.