Corregir modelos de IA

backend/app/main.py

@@ -1131,11 +1131,21 @@ def create_ai_configuration(
     # Desactivar configuraciones anteriores
     db.query(models.AIConfiguration).update({"is_active": False})
     
+    # Determinar modelo por defecto según el proveedor si no se especifica
+    model_name = config.model_name
+    if not model_name:
+        if config.provider == "openai":
+            model_name = "gpt-4o"
+        elif config.provider == "gemini":
+            model_name = "gemini-2.5-pro"
+        else:
+            model_name = "default"
+    
     # Crear nueva configuración
     new_config = models.AIConfiguration(
         provider=config.provider,
         api_key=config.api_key,
-        model_name=config.model_name,
+        model_name=model_name,
         is_active=True
     )