[CI/Build] Add experimental AMD MI300 nightly lane (#6978)

Signed-off-by: andyluo7 <andy.luo@amd.com>

docs/contributing/ci/test_system_overview.md

@@ -182,6 +182,8 @@ CUDA **L4** (`full_model`) jobs are defined once in [`.buildkite/cuda/test-night
 - **Nightly:** scheduled `main` builds with `NIGHTLY=1` (and PR labels such as `nightly-test` / `omni-test`). Default fleet is typically H100.
 - **Pre-release:** the same L4 suite runs again on extra GPU SKUs before a release (for example B200 via `MIRROR_HW=b200`), so `full_model` coverage is not limited to the nightly machine type.
 
+AMD has an experimental, non-blocking `full_model` nightly vertical slice in [`.buildkite/amd/test-amd-nightly.yml`](https://github.com/vllm-project/vllm-omni/blob/main/.buildkite/amd/test-amd-nightly.yml). It selects ROCm Qwen3-Omni function-expansion, accuracy, documentation-example, and AITER-on smoke coverage on the MI300 pool. AMD-only PR validation uses `amd-test` to admit the external AMD pipeline and `nightly-test` to select this suite; scheduled `main` builds select it with `NIGHTLY=1`. Keep it non-blocking while the lane accumulates stability and completion-time evidence.
+
 How count-form `mirror_hardwares` and `MIRROR_HW` pick a SKU: [CI Settings](./ci_settings.md).
 
 ### L2 / L3 diff-aware CI (CUDA)