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.

review_proofs.py

@@ -4803,6 +4803,13 @@ def assess_final_report_validator(report_text, task_kind, **kwargs):
     return _validate(report_text, task_kind, **kwargs)
 
 
+def assess_review_final_report_schema(report_text, **kwargs):
+    """#391: reviewer final-report schema verification before session output."""
+    from review_final_report_schema import assess_review_final_report_schema as _assess
+
+    return _assess(report_text, **kwargs)
+
+
 _QUEUE_STATUS_REPORT_HINT = re.compile(
     r"queue[- ]status|selected pr:\s*none|no pr selected|"
     r"queue[- ]status[- ]only",