feat(harness,rag): dual LLM audit fields, run conclusion, and hybrid quality

Persist provider reasoning and assistant text separately on agent_reasoning_audit
(DeepSeekAssistantMessage path), extract diagnosis_run.conclusion, enrich RAG
tool audit (step_id/query/qualityScore), gate empty mysql tools, drop devtools,
and align MVP docs after live E2E verification.

openspec/changes/archive/2026-07-28-rag-eval-hybrid-baseline/brief.md

@@ -0,0 +1,13 @@
+# Brief: rag-eval-hybrid-baseline
+
+## Background
+
+Offline RAG eval structure is correct but generator/docs/fixtures predate hybrid search mode.
+
+## Goals
+
+Knife 1 only: `search.mode` wiring, fixture meta, README, best-effort fixture refresh.
+
+## Non-goals
+
+Dual dense/hybrid fixture trees; golden mustNot/chunk/level hard gates; new frameworks.