Added handling for ProviderType.OPENROUTER in _create_provider_llm in src/cleveragents/providers/registry.py to resolve ValueError: Unsupported provider type when using OpenRouter via create_llm.
Created features/openrouter_provider_registry.feature with 11 scenarios validating OpenRouter provider behavior in ProviderRegistry.
Created features/steps/openrouter_provider_registry_steps.py with step definitions for the new feature file.
Created docs/reference/providers.md with comprehensive documentation including the OpenRouter configuration guide.
ISSUES CLOSED: #8907
