- Relaxed Gemini model validation to allow any model starting with gemini-, gemma-, or learnlm- prefixes
- This prevents breakage when new Gemini models are released
- The Google SDK will surface a clear error if a model truly doesn't exist
- Added comprehensive tests for new preview models, case-insensitive validation, and fallback behavior
- Fixes issue #3949
Co-Authored-By: João <joao@crewai.com>