docs: keep design reorg arrangement-only

Signed-off-by: Hongsheng Liu <liuhongsheng4@huawei.com>

docs/.nav.yml

@@ -144,11 +144,6 @@ nav:
       - Orchestration:
         - Entrypoint Module: design/module/entrypoint_module.md
         - AsyncOmni Architecture: design/module/async_omni_architecture.md
-    - RFCs and Experimental Work:
-      - AR-Diffusion Pipeline Capability: design/ar_diffusion_pipeline_capability.md
-      - Diffusion Operator Boundary (RFC): design/diffusion_ops.md
-      - Unified Error Handling (RFC): design/unified_error_handling.md
-      - Production-Grade NVIDIA Blackwell Support (RFC): design/blackwell_production_support.md
   - Docs Guide: contributing/DOCS_GUIDE.md
 - API Reference:
   - api/README.md