updated openrouter to randomly route between models

src/api/models/provider_models.py

@@ -56,7 +56,7 @@ class ModelRegistry(BaseModel):
 MODEL_REGISTRY = ModelRegistry(
     models={
         "openrouter": ModelConfig(
-            primary_model="openai/gpt-oss-20b:free",
+            primary_model="openrouter/free",
             candidate_models=[
                 # "meta-llama/llama-4-scout:free",
                 "cognitivecomputations/dolphin-mistral-24b-venice-edition:free",