chore(xaf-hub): lan-248 配置模型应用链 model_chain 4 档

opencode/deepseek-v4.1-flash-free -> axonhub/deepseek ->
nvidia/nvidia/nemotron-3-ultra-550b-a55b -> agnes/agnes-3.0-flash

用户 2026-11-03 拍板指定顺序；映射说明：
- opencode/deepseek-free -> opencode/deepseek-v4.1-flash-free（对齐 default_dispatch_model 既有写法）
- nivdia/nemotron 3 ultra 550B A55B -> nvidia/nvidia/nemotron-3-ultra-550b-a55b（修正拼写，对齐 lan-189 既有写法）
- agnes/agnes-3.0-flash -> 原样

tools/xaf_agent_hub/config.json

@@ -64,7 +64,13 @@
         "/sc-data/cfc"
       ],
       "default_directory": "/sc-data/cfc",
-      "fallback_model": "axonhub/deepseek"
+      "fallback_model": "axonhub/deepseek",
+      "model_chain": [
+        "opencode/deepseek-v4.1-flash-free",
+        "axonhub/deepseek",
+        "nvidia/nvidia/nemotron-3-ultra-550b-a55b",
+        "agnes/agnes-3.0-flash"
+      ]
     },
     {
       "name": "lan-204",