Unify Qwen3-VL registry and config key

config.yaml

@@ -48,6 +48,7 @@ model:
     ffn_dim: 4096
     shift_action: 5.0
   vlm_backbone:
+    name: qwen3_vl_2b
     checkpoint_path: /path/to/Qwen3-VL-2B-Instruct
     load_pretrained: true
     max_length: 512