swap: Gemma 4 31B as primary, Qwen3 Coder as fallback

- Primary: google/gemma-4-31b-it (native FC, 256K ctx)
- Fallback: qwen/qwen3-coder (480B MoE, strong coding)

config.yaml

@@ -1,8 +1,8 @@
-model: qwen/qwen3-coder
+model: google/gemma-4-31b-it
 provider: openrouter
 fallback_model:
   provider: openrouter
-  model: google/gemma-4-31b-it
+  model: qwen/qwen3-coder
 max_turns: 90
 platforms:
   feishu: