feat: enhance LLM model creation with optional default pipeline setting

- Updated create_llm_model method to include auto_set_to_default_pipeline parameter.
- Adjusted ModelManager to set auto_set_to_default_pipeline to False when creating models.
- Improved logic for setting the default pipeline model based on the new parameter.

src/langbot/pkg/provider/modelmgr/modelmgr.py

@@ -149,6 +149,7 @@ class ModelManager:
                         'prefered_ranking': space_model.featured_order,
                     },
                     preserve_uuid=True,
+                    auto_set_to_default_pipeline=False,
                 )
 
             elif space_model.category == 'embedding':