Set TORCH_CUDA_ARCH_LIST for SageAttention build

Build runner has no GPU, so specify target architectures explicitly.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Dockerfile

@@ -65,6 +65,8 @@ WORKDIR /tmp
 ENV EXT_PARALLEL=4
 ENV NVCC_APPEND_FLAGS="--threads 8"
 ENV MAX_JOBS=32
+# Target RunPod GPU architectures: A100(8.0), RTX 30xx(8.6), RTX 40xx(8.9), H100(9.0)
+ENV TORCH_CUDA_ARCH_LIST="8.0;8.6;8.9;9.0"
 RUN git clone https://github.com/thu-ml/SageAttention.git && \
     cd SageAttention && \
     pip install --no-build-isolation . && \