feat(eval): Chat Eval Pipeline Phase 1-4 + fix

[mangowhoiscloud]

Summary

• Phase 1: Domain + Application layer (EvalResult VO, EvalConfig DTO, L1/L2/L3 서비스)
• Phase 2: BARS prompts, LangGraph eval subgraph (Send API fan-out), main graph 통합
• Phase 3: Gateway adapters (Redis + PG composite), DI wiring, V005 migration, calibration fixture
• Phase 4: PG pool DI (asyncpg), SSE eval stage, structured logging, eval-feedback-loop skill
• Fix: 누락된 persistence 어댑터, calibration fixture, 단위 테스트, factory wiring 추가

Key Numbers

• 36 files across Domain/Application/Infrastructure layers
• 165 tests ALL PASS (pytest -m eval_unit)
• 5-expert review loop: Design R5(99.8) / Code R2(97.1)

Architecture

• Swiss Cheese 3-Tier: L1 Code Grader → L2 LLM BARS Grader → L3 Calibration CUSUM
• Clean Architecture: Port/Adapter, CQRS (Command/Query Gateway), frozen VO
• FAIL_OPEN: eval 실패 시 B-grade(65.0) fallback, 사용자 응답 차단 없음

Test plan

• pytest -m eval_unit -v --tb=short — 165 tests ALL PASS
• black --check && ruff check — CI lint clean
• Redis-only 모드 동작 확인 (eval_postgres_dsn 비어있을 때)
• SSE 이벤트에 eval 단계 표시 확인
• enable_eval_pipeline=True 기본 동작 확인

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