fix(setup): install mlx-lm and mlx-audio in setup-python on Apple Silicon (#892)

* fix(setup): install mlx-lm and mlx-audio in setup-python on Apple Silicon

The dev setup installed requirements-mlx.txt but not mlx-audio/mlx-lm
themselves, so POST /transcribe failed on a fresh Apple Silicon setup
with "No module named 'mlx_audio'" (then "No module named 'mlx_lm'").
The release workflow already installs both with --no-deps (they declare
transformers>=5.x, conflicting with our <=4.57.x cap); mirror that in
the setup-python recipe with the same pins.

Co-Authored-By: Claude Fable 5 <[email protected]>

* test: add MLX smoke test for the --no-deps mlx-audio/mlx-lm install

mlx-audio and mlx-lm are installed --no-deps, so a missing transitive
dependency only surfaces at import time. Add a pytest-discoverable
smoke test (skipped off Apple Silicon) covering the exact entry points
the backend uses: mlx_audio.tts.load, mlx_audio.stt.load (which also
exercises the miniaudio dep from issue #505), mlx_lm.load/generate,
and a basic mlx.core op.

Co-Authored-By: Claude Fable 5 <[email protected]>

---------

Co-authored-by: Claude Fable 5 <[email protected]>

justfile

@@ -72,6 +72,12 @@ setup-python:
     if [ "$(uname -m)" = "arm64" ] && [ "$(uname)" = "Darwin" ]; then
         echo "Detected Apple Silicon — installing MLX dependencies..."
         {{ pip }} install -r {{ backend_dir }}/requirements-mlx.txt
+        # mlx-lm and mlx-audio declare transformers>=5.x, which conflicts with
+        # our transformers<=4.57.x cap, so install them --no-deps (their other
+        # runtime deps are covered by requirements.txt / requirements-mlx.txt —
+        # see the note in requirements-mlx.txt and .github/workflows/release.yml)
+        {{ pip }} install --no-deps mlx-lm==0.31.1
+        {{ pip }} install --no-deps mlx-audio==0.4.1
     fi
     {{ pip }} install git+https://github.com/QwenLM/Qwen3-TTS.git
     {{ pip }} install pyinstaller ruff pytest pytest-asyncio -q