Add RoutingEngineService that classifies tasks, evaluates routing rules
in priority order, checks provider health, and applies a Sonnet → Haiku
→ Ollama fallback chain when no healthy rule match is found.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
Adds comprehensive integration tests at apps/gateway/src/agent/__tests__/provider-adapters.test.ts
verifying adapter registration, graceful degradation without API keys, the capability
matrix, ProviderService integration, and ProviderCredentialsService encryption logic.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>