When a model search returns no results for a specific base_model, retry the
same query with base_model_context=None so the provider can match any model.
Fallback matches are marked with any_model_match and base_model_fallback on
the result payload. The UI reports 'Found (Any Model)' when a result came
from this fallback path, and the cancel/progress button styling is tightened
to 16x16px with border-radius.