Update model registry and documentation

- Corrected model family naming conventions in models.json for Claude and Gemini models.
- Removed unnecessary input/output modalities for several models in models.json.
- Updated context windows and max output tokens for various models in models.json.
- Consolidated Gemini model names for clarity and consistency.
- Enhanced models documentation in models_docs.rake to include links to the model registry and detailed contribution guidelines.

Author: crmne