feat: require transient validation failure history in reviewer reports (Closes #396)

Add assess_validation_failure_history_report so reviewer final reports must
document every validation failure observed during a session, not only the
final passing result. Wire the verifier into final_report_validator,
gitea_validate_review_final_report, and the review-merge workflow template.

Co-Authored-By: Claude Opus 4.8 (1M context) <[email protected]>

gitea_mcp_server.py

@@ -1244,7 +1244,7 @@ def gitea_create_pr(
     )
     if blocked:
         return blocked
-    verify_preflight_purity(remote)
+    verify_preflight_purity(remote, worktree_path=worktree_path)
     h, o, r = _resolve(remote, host, org, repo)
 
     # ── Issue Lock Validation (Issue #194 / #196) ──
@@ -5504,6 +5504,7 @@ def gitea_validate_review_final_report(
     action_log: list[dict] | None = None,
     mutations_observed: bool = False,
     local_edits: bool = False,
+    validation_session: dict | None = None,
 ) -> dict:
     """Read-only: machine-validate reviewer final report schema before output (#391).
 
@@ -5521,6 +5522,7 @@ def gitea_validate_review_final_report(
         action_log=action_log,
         mutations_observed=mutations_observed,
         local_edits=local_edits,
+        validation_session=validation_session,
     )