feat(llm): add Perplexity, Gemini providers and createFallbackChain
- Add PerplexityProvider (OpenAI-compatible, reads PERPLEXITY_API_KEY)
- Add GeminiProvider (Google Generative Language API adapter, reads GEMINI_API_KEY)
- Add createFallbackChain() — ordered provider chain, skips unconfigured,
aggregates errors; allows any app to replace custom LLM fallback loops
- Extend LLMProviderType with 'perplexity' | 'gemini'
- Update factory to resolve and instantiate new provider types
- Add PAID_PROVIDERS to llm-router registry (OpenAI, Perplexity) for apps
using round-robin routing alongside free-tier providers
- 27 tests covering fallback chain, new providers, error/edge cases
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
Saravana Achu Mac
43bf51a290