[Refactor] Migrate Legacy Stage Configs to the Pipeline Registry (#5031)

Signed-off-by: zwhzzz0821 <2831474076@qq.com>
Co-authored-by: zwhzzz0821 <zwhzzz0821@users.noreply.github.com>
Co-authored-by: SYLAR <125541396+lishunyang12@users.noreply.github.com>
Co-authored-by: Hongsheng Liu <liuhongsheng4@huawei.com>

docs/contributing/model/adding_omni_model.md

@@ -34,6 +34,7 @@ vllm_omni/model_executor/models/
 └── your_model_name/              # Model directory (e.g., qwen3_omni)
     ├── __init__.py               # Exports main model class
     ├── your_model.py             # Main unified model class
+    ├── pipeline.py               # Pipeline topology registry entry
     ├── your_model_stage1_implementation.py      # Stage 1 implementation (e.g., thinker)
     ├── your_model_stage2_implementation.py      # Stage 2 implementation (e.g., talker)
     └── your_model_stage3_implementation.py      # Stage 3 implementation (e.g., code2wav)
@@ -42,10 +43,14 @@ vllm_omni/model_executor/models/
 vllm_omni/model_executor/stage_input_processors/
 └── your_model_name.py            # Stage transition processors
 
-vllm_omni/model_executor/stage_configs/
-└── your_model_name.yaml          # Stage configuration file
+vllm_omni/deploy/
+└── your_model_name.yaml          # Deployment configuration file
 ```
 
+New in-tree models should register their `PipelineConfig` in
+`vllm_omni/config/pipeline_registry.py`; use `--stage-configs-path` only for
+custom legacy `stage_args` YAMLs.
+
 ## Step-by-Step Implementation
 
 ### Step 1: Create the Model Directory