Add and update tests for the catalogs and schemas endpoints to verify:
- Default catalog/schema is returned when accessible
- Default is null when not in user's accessible list
- Default is null when retrieval fails (error handling)
- Default works correctly with upload_allowed filter
- Default is null when not in upload-allowed schemas list
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Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>