Add Hygon BW200 DCU knowledge base documentation
- Add comprehensive hygon-bw200-dcu.md guide with:
- Architecture specs (CDNA2, gfx90a, 80 CUs, 64GB HBM2e)
- Live system snapshot from 8-GPU deployment
- HIP programming examples and kernel launch configs
- Multi-GPU RCCL collectives guide
- Performance optimization (occupancy, LDS, MFMA)
- Monitoring commands (rocm-smi, rocprof)
- DTK/ROCm compatibility notes
- Update cdna-architecture.md with BW200 in CDNA2 section
- Update INDEX.md with BW200 layer-1 hardware entry
Co-Authored-By: Claude Opus 4.8 noreply@anthropic.com