Fix Qwen3-Omni MoE backend selection

Signed-off-by: hsliuustc0106 <liuhongsheng4@huawei.com>

docs/user_guide/examples/online_serving/qwen3_omni.md

@@ -17,9 +17,9 @@ vllm serve Qwen/Qwen3-Omni-30B-A3B-Instruct --omni --port 8091
 
 The default deployment configuration situated at `vllm_omni/deploy/qwen3_omni_moe.yaml` is resolved and loaded
 automatically via the model registry, obviating the necessity for the `--deploy-config` flag in standard deployment topologies.
-The bundled Qwen3-Omni setup defaults `VLLM_USE_FLASHINFER_MOE_FP16=0`. This keeps the Thinker & Talker on vLLM's
-Triton unquantized MoE path and avoids the performance regression observed with the FlashInfer CUTLASS unquantized MoE
-backend.
+The bundled Qwen3-Omni setup explicitly sets `moe_backend: triton` for the Thinker and Talker stages. This keeps
+both stages on vLLM's Triton unquantized MoE path and avoids the unstable FlashInfer CUTLASS unquantized MoE path on
+some GPUs.
 Asynchronous chunk streaming is **enabled by default** within the bundled configuration.
 
 To explicitly utilize a custom deployment YAML, specify the configuration path:
@@ -87,15 +87,9 @@ vllm serve Qwen/Qwen3-Omni-30B-A3B-Instruct --omni --port 8091 \
     --stage-overrides '{"1": {"gpu_memory_utilization": 0.5}}'
 ```
 
-To experiment with the FlashInfer FP16 MoE path, set `VLLM_USE_FLASHINFER_MOE_FP16=1` before launching the server:
-```bash
-VLLM_USE_FLASHINFER_MOE_FP16=1 \
-vllm serve Qwen/Qwen3-Omni-30B-A3B-Instruct --omni --port 8091
-```
-
-For the stage-based CLI, you usually do **not** need `--stage-overrides` for
-that kind of change. Since each command launches one stage, just pass the knob
-directly on that stage command:
+To experiment with another supported MoE backend, set `moe_backend` in the
+deployment YAML for both the Thinker and Talker stages. For the stage-based
+CLI, pass `--moe-backend` directly on each stage command.
 
 ```bash
 CUDA_VISIBLE_DEVICES=1 vllm serve Qwen/Qwen3-Omni-30B-A3B-Instruct --omni \