Switch to ROCm 6.4 + Python 3.11 + PyTorch 2.9.1

- Base image: rocm/dev-ubuntu-22.04:6.4
- Python 3.10 → 3.11 via deadsnakes PPA
- torch/torchaudio: 2.5.1 → 2.9.1 (rocm6.4 wheel index)
- torchvision: 0.20.1 → 0.24.1
- pytorch_triton_rocm: 3.1.0 → 3.5.1

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

requirements-rocm-init.txt

@@ -1,5 +1,5 @@
---index-url https://download.pytorch.org/whl/rocm7.2
-torch==2.11.0
-torchaudio==2.11.0
-torchvision==0.26.0
-pytorch_triton_rocm==3.3.0
+--index-url https://download.pytorch.org/whl/rocm6.4
+torch==2.9.1
+torchaudio==2.9.1
+torchvision==0.24.1
+pytorch_triton_rocm==3.5.1