fix(docker): fix startup crash and permission errors in the container

Four related fixes uncovered while getting Docker running on a Linux
host without AVX-512 and with an NVIDIA GPU:

- pedalboard>=0.9.21 ships a Linux wheel with AVX-512 instructions
  baked into its native extension, which SIGILLs (exit 132) on import
  on any CPU without AVX-512 support. Pin below the regression until
  upstream fixes it (spotify/pedalboard#454).
- The rocminfo probe in app.py ran unconditionally on every build
  variant, always failing and logging on non-ROCm systems. Gate it on
  /dev/kfd actually being present.
- sox (required by qwen-tts's X-vector extractor) and a C compiler
  (required by Triton to JIT-compile its CUDA driver shim on first
  use) were missing from the runtime image, causing hard failures
  once those code paths were actually exercised.
- Named volumes and bind mounts (HF cache, app data, generated audio)
  are created root-owned by Docker on first use, but the app runs as
  the unprivileged voicebox user. chown the mount points in the
  entrypoint before dropping privileges so this self-heals on every
  start regardless of host UID.

backend/app.py

@@ -49,7 +49,7 @@ if not os.environ.get("HSA_OVERRIDE_GFX_VERSION"):
 # Only set HSA_OVERRIDE_GFX_VERSION for older GPUs that need it.
 # RDNA 3+ (gfx1100+) and RDNA 4 (gfx1200+) are natively supported by ROCm
 # and the override can cause suboptimal performance or errors.
-if not os.environ.get("HSA_OVERRIDE_GFX_VERSION"):
+if not os.environ.get("HSA_OVERRIDE_GFX_VERSION") and Path("/dev/kfd").exists():
     try:
         result = subprocess.run(
             ["rocminfo"],

backend/requirements.txt

@@ -58,7 +58,11 @@ librosa>=0.10.0
 soundfile>=0.12.0
 numpy>=1.24.0,<2.0
 numba>=0.60.0,<0.61.0
-pedalboard>=0.9.0
+# pedalboard>=0.9.21 ships a Linux wheel with AVX-512 (zmm) instructions baked
+# into its native extension, which SIGILLs on import on any CPU without
+# AVX-512 (e.g. Zen 2/3, pre-Ice-Lake Intel). Pin below the regression until
+# upstream fixes it: https://github.com/spotify/pedalboard/issues/454
+pedalboard>=0.9.0,<0.9.21
 
 # HTTP client (for CUDA backend download)
 httpx>=0.27.0