Fix config_loader documentation inconsistencies

- Correct overview.md to focus on dictionary-based configuration
- Remove file-based loading hallucinations
- Update agent-config.md with accurate API examples
- Add missing Swarm-as-Tool and Graph-as-Tool examples to tool-config.md
- Correct structured-output.md to match implementation
- Update swarm-config.md and graph-config.md with proper usage
- Clarify experimental nature throughout documentation
- Ensure all examples match actual public interface
- Remove references to non-existent features

Author: vawsgit