feat: add reviewer final-report schema MCP validator (Closes #391)

Expose gitea_validate_review_final_report composing the composable
final-report validator with review-specific schema gates for legacy
fields, merge/issue claims, blocked handoff replay, and narrative drift.

tests/test_llm_workflow_split.py

@@ -136,6 +136,12 @@ def test_final_report_validator_exported():
     assert callable(assess_final_report_validator)
 
 
+def test_review_final_report_schema_verifier_exported():
+    from review_proofs import assess_review_final_report_schema
+
+    assert callable(assess_review_final_report_schema)
+
+
 def test_create_issue_final_report_verifier_exported():
     from review_proofs import assess_create_issue_final_report