Add diagnosis eval harness

mvp/eval/README.md

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+# Diagnosis Eval Harness
+
+This folder contains the first fixed-case evaluation set for the MVP diagnosis Agent.
+
+## Scope
+
+- Case definitions: `cases/diagnosis-cases.json`
+- Offline trace fixtures: `fixtures/*.json`
+- Field definitions: `schema.md`
+- Evaluator implementation: `DiagnosisTraceEvaluator`
+- Report writer: `DiagnosisEvalReportWriter`
+
+## Current Mode
+
+The first version evaluates saved trace fixtures. It does not start the application and does not require MySQL, Redis, Milvus, or a real LLM.
+
+## Verification
+
+Run the focused evaluator test:
+
+```powershell
+mvn -q "-Dtest=DiagnosisTraceEvaluatorTest" test
+```
+
+## Interview Story
+
+The harness gives the MVP a repeatable baseline:
+
+```text
+fixed diagnosis case
+-> saved or runtime trace
+-> rule-based trace validation
+-> JSON / Markdown report
+-> regression signal for prompts, tools, retrieval, and verifier behavior
+```