Add comprehensive input documentation for agents

Introduce detailed documentation on how input works for agents, including flow, formats, examples, validation, and testing procedures. Update references in the README and agents documentation to link to this new resource.

README.md

@@ -109,6 +109,7 @@ Comprehensive documentation is available in the [docs](./docs) directory:
 - [API Documentation](./docs/api.md) - API endpoints and usage examples
 - [Authentication](./docs/tokens.md) - Authentication system documentation
 - [Agents Guide](./docs/agents.md) - How to create and use agents
+- [Input Documentation](./docs/input.md) - How input works for agents
 
 ## License