fix(docker): add ROCm GPU support via compose overlay (#630)

* fix(docker): add ROCm GPU support via compose overlay

Fixes #618. The Docker image installs CPU-only PyTorch from PyPI by
default, so even when users correctly pass /dev/kfd and /dev/dri device
nodes into the container, torch.cuda.is_available() returns False and
the GPU is reported as "None (CPU only)".

Changes:
- Dockerfile: add PYTORCH_VARIANT build arg (default: cpu). When set to
  "rocm", the ROCm-enabled PyTorch wheels are installed from the
  pytorch.org/whl/rocm6.3 index before requirements.txt runs, so pip
  sees the ROCm build as already satisfying the torch>=2.2.0 constraint
  and does not overwrite it with the CPU wheel. The render and video
  groups are created with parameterised GIDs (RENDER_GID / VIDEO_GID,
  defaulting to Ubuntu 22.04 values) and the voicebox user is added to
  both groups so it can open /dev/kfd and /dev/dri.

- docker-compose.rocm.yml: new compose overlay that wires everything
  together — PYTORCH_VARIANT=rocm build arg, /dev/kfd + /dev/dri device
  passthrough, group_add for render/video, HSA_OVERRIDE_GFX_VERSION
  (defaults to 11.0.0 for RDNA3/Strix Halo with a comment listing
  values for RDNA2/RDNA1/Vega), and PYTORCH_HIP_ALLOC_CONF for the
  memory allocator. Usage:
    docker compose -f docker-compose.yml -f docker-compose.rocm.yml up --build

- docker-compose.yml: add a comment pointing to the ROCm overlay.

The CPU default path is unchanged — no extra build time, no size increase.

Co-authored-by: Cursor <[email protected]>

* fix(docker): address review comments on ROCm overlay

Two issues raised in PR review:

1. CodeRabbit: `docker compose up --build-arg` is not supported by the
   `up` subcommand. Replaced the GID override instructions with the
   correct env-var export pattern. Added RENDER_GID and VIDEO_GID to
   `build.args` using ${VAR:-default} interpolation so a single export
   covers both the Dockerfile group creation and the runtime group_add.
   Changed group_add entries from hardcoded strings to the same
   interpolated vars so host GIDs stay in sync end-to-end.

2. @Xarianne: ROCm 6.3 does not support RDNA 4 (RX 9000 series) cards.
   Added a ROCM_VERSION build arg (default 6.3) to both the Dockerfile
   and docker-compose.rocm.yml so users can set ROCM_VERSION=7.2 for
   RDNA 4 support without editing any files. Added RDNA 4 / 12.0.0 to
   the HSA_OVERRIDE_GFX_VERSION comment table.

Co-authored-by: Cursor <[email protected]>

---------

Co-authored-by: Cursor <[email protected]>

docker-compose.yml

@@ -1,3 +1,7 @@
+# Voicebox — CPU build (default)
+# For AMD ROCm GPU acceleration use the overlay:
+#   docker compose -f docker-compose.yml -f docker-compose.rocm.yml up --build
+
 services:
   voicebox:
     build: .