fix: Wan2.1 use /v1/videos (async), /v1/videos/sync not in v0.18.0

Verified on L40S with SM image:
- Model loads and serves on g6e.xlarge (L40S 48GB)
- /v1/videos returns queued job with id
- Middleware routes /invocations -> /v1/videos with form data

Author: Yadan Wei

.github/config/vllm-omni-model-tests.yml

@@ -33,7 +33,7 @@ smoke-test:
       s3_model: "wan2.1-t2v-1.3b.tar.gz"
       fleet: "x86-g6exl-runner"
       extra_args: ""
-      route: "/v1/videos/sync"
+      route: "/v1/videos"
       content_type: "multipart/form-data"
       test_request: 'prompt=a dog running on a beach&num_frames=17&num_inference_steps=4&size=480x320&seed=42'
       validate: "binary_size_gt:1000"