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.

skills/llm-project-workflow/workflows/reconcile-landed-pr.md

@@ -304,6 +304,40 @@ If any required mutation capability is missing:
 * include safe next action (profile switch, human close, or dedicated reconciler
   profile)
 
+## 15A. Audit vs cleanup phase (#419)
+
+Reconciliation audits are **read-only** unless a separate cleanup phase is
+explicitly authorized.
+
+**Audit phase forbids** (``audit_reconciliation_mode.check_audit_mutation_allowed``
+fails closed):
+
+* ``gitea_delete_branch``
+* ``git branch -D``
+* ``git worktree remove``
+* pushes
+* issue/PR mutations
+* file edits
+
+Dry-run merged-cleanup reconciliation (``gitea_reconcile_merged_cleanups`` with
+``dry_run=True``) stays in audit phase. Execution requires:
+
+1. Operator approval or workflow authorization
+2. Exact ``delete_branch`` capability proof (``gitea.branch.delete``)
+3. Proof branch/worktree is safe to remove
+4. Before/after state snapshot
+
+Call ``gitea_authorize_reconciliation_cleanup_phase`` before any cleanup
+mutation. Final reports must not claim ``no mutations`` if cleanup occurred.
+Classify cleanup mutations as:
+
+* remote branch deletion → **External-state mutations**
+* local branch deletion → **Git ref mutations**
+* worktree removal → **Cleanup mutations**
+
+``audit_reconciliation_mode.assess_audit_reconciliation_report`` validates
+these boundaries in final reports.
+
 ## 16. Mutation classification
 
 Use precise mutation categories in the final report: