bug: 🐛 Improve error managing in audio-summarizer-assistant example

[philippart-s]

If an error occurs during the API call, this error is raised:

$ python audio-summarizer-app.py
* Running on local URL:  http://0.0.0.0:8000
* To create a public link, set `share=True` in `launch()`.
Error: 404
Traceback (most recent call last):
  File "/usr/local/lib/python3.13/site-packages/gradio/queueing.py", line 625, in process_events
    response = await route_utils.call_process_api(
               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    ...<5 lines>...
    )
    ^
  File "/usr/local/lib/python3.13/site-packages/gradio/route_utils.py", line 322, in call_process_api
    output = await app.get_blocks().process_api(
             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    ...<11 lines>...
    )
    ^
  File "/usr/local/lib/python3.13/site-packages/gradio/blocks.py", line 2191, in process_api
    result = await self.call_function(
             ^^^^^^^^^^^^^^^^^^^^^^^^^
    ...<8 lines>...
    )
    ^
  File "/usr/local/lib/python3.13/site-packages/gradio/blocks.py", line 1702, in call_function
    prediction = await anyio.to_thread.run_sync(  # type: ignore
                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
        fn, *processed_input, limiter=self.limiter
        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    )
    ^
  File "/usr/local/lib/python3.13/site-packages/anyio/to_thread.py", line 56, in run_sync
    return await get_async_backend().run_sync_in_worker_thread(
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
        func, args, abandon_on_cancel=abandon_on_cancel, limiter=limiter
        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    )
    ^
  File "/usr/local/lib/python3.13/site-packages/anyio/_backends/_asyncio.py", line 2470, in run_sync_in_worker_thread
    return await future
           ^^^^^^^^^^^^
  File "/usr/local/lib/python3.13/site-packages/anyio/_backends/_asyncio.py", line 967, in run
    result = context.run(func, *args)
  File "/usr/local/lib/python3.13/site-packages/gradio/utils.py", line 894, in wrapper
    response = f(*args, **kwargs)
  File "/mnt/audio-summarizer-app.py", line 59, in asr_transcription
    return resp
           ^^^^
UnboundLocalError: cannot access local variable 'resp' where it is not associated with a value 

It should be more usable to have the HTTP error code and messages.