feat: gate reconciliation audit mode from unauthorized cleanup (Closes #419)

Add audit vs cleanup phase tracking so reconciliation audits stay read-only
unless cleanup is explicitly authorized with delete capability proof, safety
proof, and before/after snapshots. Block gitea_delete_branch and merged-cleanup
execution during audit phase, validate final reports for false no-mutations
claims, and document the boundary in the reconcile-landed-pr workflow.

final_report_validator.py

@@ -919,6 +919,22 @@ def _rule_shared_author_reviewer_same_run(report_text: str) -> list[dict[str, st
     )
 
 
+def _rule_audit_reconciliation_boundary(report_text: str) -> list[dict[str, str]]:
+    from audit_reconciliation_mode import assess_audit_reconciliation_report
+
+    result = assess_audit_reconciliation_report(report_text)
+    if result.get("proven"):
+        return []
+    return _findings_from_reasons(
+        "reconcile.audit_cleanup_boundary",
+        result.get("reasons") or [],
+        field="Audit/cleanup phase",
+        severity="block",
+        safe_next_action=result.get("safe_next_action")
+        or "separate audit from authorized cleanup and classify mutations",
+    )
+
+
 def _rule_reviewer_review_mutation(
     report_text: str,
     *,
@@ -977,6 +993,7 @@ _RULES_BY_TASK: dict[str, list[Callable[..., list[dict[str, str]]]]] = {
         _rule_reviewer_git_fetch_readonly,
         _rule_reviewer_legacy_workspace_mutations,
         _rule_reviewer_vague_mutations_none,
+        _rule_audit_reconciliation_boundary,
     ],
     "author_issue": [
         _rule_shared_controller_handoff,