test(agentic-rag): add comprehensive unit tests for auth, llm_factory, and providers
## Added
- test_auth.py: 19 tests for JWT, API Key, password hashing, and auth flow
- test_llm_factory.py: 21 tests for all 8 LLM providers
- test_providers.py: API route tests for provider management
## Coverage
- Password hashing with bcrypt
- JWT token creation/validation/expiration
- API key verification (admin key)
- Dual-mode authentication (API key + JWT)
- Z.AI, OpenCode Zen, OpenRouter client implementations
- Factory pattern for all providers
- Client caching mechanism
All 40+ tests passing ✅
437a484b1c