Start v2 safety hardening

fix: MistralJudge schema detection for truths/claims/verdicts — matches DeepEval 3-call pattern (Day 15)

fix: MistralJudge uses from_json_schema grammar — correct structure for claim extraction and verification (Day 15)

fix: GBNF grammar-constrained JSON sampling in MistralJudge — eliminates DeepEval JSON parse errors (Day 15)

fix: MistralJudge JSON extraction for DeepEval faithfulness, commit Wilcoxon results (Day 15)

feat: DeepEval FaithfulnessMetric with Mistral judge, async_mode=False (replaces RAGAS, Day 15)

fix: guardrail dual-import path, bertscore key names, ragas reuse pipeline.llm (Day 14)

feat: eval scripts — BM25 baseline, adversarial probes, BERTScore, RAGAS, Wilcoxon (Day 14)