The riva-asr/nmt/tts client scripts historically exit 0 on most error
paths — including "Unavailable model", connection refused, empty/invalid
input, and missing files — which causes CI pipelines composing these
scripts via && chains to silently swallow real failures.

Add a cli_main decorator that translates uncaught exceptions into a
small, consistent set of exit codes:

  2 = bad input (missing/empty file, ValueError, IsADirectoryError)
  3 = gRPC UNAVAILABLE (server down, wrong port, network)
  4 = gRPC INVALID_ARGUMENT / NOT_FOUND (bad model/lang/voice)
  1 = anything else
  130 = SIGINT

The decorator also writes the error to stderr so CI logs surface the
cause rather than the script swallowing it. Follow-up commit wires
this into each client script.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

…ation

Address the VDR 26.02 finding that python-clients CLIs exit 0 on most
error paths across all three modalities. Each script now:

  - Wraps main() with @cli_main so gRPC and OS errors propagate to a
    real exit code instead of being printed and swallowed.
  - Calls sys.exit(main()) so the chosen exit code reaches the shell.

Script-specific fixes:

  scripts/nmt/nmt.py
    - Drop the inner request() try/except that swallowed every gRPC
      status; let cli_main translate it. Empty/whitespace --text and
      missing --text-file now return EXIT_BAD_INPUT (was: silent
      exit 0). Document --max-len-variation as decoder-token units
      with valid range [0, 256], default 20, and Arabic chunking note.

  scripts/tts/talk.py
    - Reject whitespace-only --text up front (defense-in-depth pair to
      the server-side fix in riva-speech that closed the hang on
      `--text "   "`). Drop the broad `except Exception` that
      stringified gRPC errors and exited 0.

  scripts/asr/transcribe_file*.py
    - Replace `print(...); return` on missing input files with
      EXIT_BAD_INPUT. Remove the silent grpc.RpcError swallow in
      transcribe_file_offline.py.

  scripts/asr/transcribe_mic.py + realtime_asr_client.py + tts/talk.py
    - Pyaudio install hint now mentions `apt-get install -y
      portaudio19-dev` (Debian/Ubuntu) and `brew install portaudio`
      (macOS), pairing with the prereqs doc landed in documentation_2.

  scripts/tts/realtime_tts_client.py
    - Drop the module-level `from riva.client.audio_io import
      SoundCallBack` import (it was unused and pulled pyaudio in
      eagerly, defeating the lazy import). Drop the broad
      `except Exception` that mapped every failure to exit 1.

  scripts/nmt/nmt_speech_to_{text,speech}.py
    - Drop unused `import grpc`; remove the catch-all that printed
      "Error during translation" and exited 0.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>