Remove duplicate Runtime Fallback section from configurations.md. Fix max_fallback_attempts range from (1-10) to (1-20) to match schema. Update retry_on_errors default to include 400 status code. Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-opencode) Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>