Add optional OpenRouter Jev decisions routing

[1vav]

Summary

• Add an off-by-default OpenRouter Jev Decisions client using the documented alpha endpoint and latest model route.
• Add Anansi model settings for the Jev feature flag and model picker.
• Route response verification, issue classification, ticket-comment significance, multi-thread assignment, and context filtering through Jev with existing LLM fallbacks.
• Add synthetic offline contract and adapter tests, plus implementation and rollout documentation.

Verification

• Focused suite: 138 passed, 2 deselected. The deselected graph tests require psycopg, which is absent from this local checkout.
• Ruff and commit hooks passed.
• No funded live Jev call was run. The feature remains off by default; funded smoke tests and threshold calibration are documented release gates.