[Misc] Align CODEOWNERS with module/feature design docs (#5958)

Signed-off-by: hsliu_ustc <hsliu_ustc@noreply.gitcode.com>
Signed-off-by: Hongsheng Liu <liuhongsheng4@huawei.com>
Co-authored-by: hsliu_ustc <hsliu_ustc@noreply.gitcode.com>
Co-authored-by: Copilot Autofix powered by AI <175728472+Copilot@users.noreply.github.com>

docs/design/module/diffusion/diffusion_runtime.md

@@ -6,6 +6,7 @@ owners:
   - "@Isotr0py"
   - "@princepride"
   - "@SamitHuang"
+  - "@fhfuih"
 primary_code_paths:
   - vllm_omni/diffusion/sched/**
   - vllm_omni/diffusion/executor/**