feat(worker): add PlanningAggregator.CleanupIntegrationBranchAsync

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/ClaudeDo.Worker/Planning/PlanningAggregator.cs

@@ -112,6 +112,23 @@ public sealed class PlanningAggregator
         return new CombinedDiffResult.Ok(new CombinedDiffSuccess(integrationBranch, unifiedDiff));
     }
 
+    public async Task CleanupIntegrationBranchAsync(string planningTaskId, CancellationToken ct)
+    {
+        var (planning, repoDir, _) = await LoadPlanningContextAsync(planningTaskId, ct);
+        var branch = BuildIntegrationBranchName(planning);
+
+        var current = await _git.GetCurrentBranchAsync(repoDir, ct);
+        if (string.Equals(current, branch, StringComparison.Ordinal))
+        {
+            var branches = await _git.ListLocalBranchesAsync(repoDir, ct);
+            var target = branches.FirstOrDefault(b => b != branch && !b.StartsWith("claudedo/", StringComparison.Ordinal)) ?? "main";
+            await _git.CheckoutBranchAsync(repoDir, target, ct);
+        }
+
+        try { await _git.BranchDeleteAsync(repoDir, branch, force: true, ct); }
+        catch { /* already gone — idempotent */ }
+    }
+
     private async Task<(TaskEntity planning, string repoDir, IReadOnlyList<TaskEntity> children)>
         LoadPlanningContextAsync(string planningTaskId, CancellationToken ct)
     {