fix(chat): exclude ChatTemplateKwargs for OpenAI API

ChatTemplateKwargs parameter is only supported by custom backends
like vLLM. OpenAI API does not support this parameter and returns
400 Bad Request error.

This change conditionally includes ChatTemplateKwargs only when
the provider is ProviderGeneric (custom deployment).

Fixes connection test failure for OpenAI models with error:
"Unrecognized request argument supplied: chat_template_kwargs"

internal/models/chat/remote_api.go

@@ -204,8 +204,13 @@ func (c *RemoteAPIChat) buildChatCompletionRequest(messages []Message,
 		}
 	}
 
-	req.ChatTemplateKwargs = map[string]interface{}{
-		"enable_thinking": thinking,
+	// ChatTemplateKwargs is only supported by custom backends like vLLM.
+	// Official APIs (OpenAI, Aliyun, Zhipu, etc.) do not support this parameter
+	// and will return 400 Bad Request if it's included.
+	if c.provider == provider.ProviderGeneric {
+		req.ChatTemplateKwargs = map[string]interface{}{
+			"enable_thinking": thinking,
+		}
 	}
 
 	// Log LLM request for debugging