feat(worker): report progress for continue_merge and unit-merge verify gate

continue_merge and the parent/children unit-merge drain (PlanningMergeOrchestrator)
re-run the post-merge verify gate but never forwarded their IProgress token into it,
so a slow verify command on either path went silent past Claude Code's 300s MCP
idle-abort even though D1-D3 already fixed this for merge_task/review_task's
childless path. list_worktrees also gets elapsed-time progress: many tracked
worktrees means many concurrent git subprocess spawns.

Worker CLAUDE.md's existing progress rule now points at ProgressReporter as the
one implementation instead of a fresh polling loop.

src/ClaudeDo.Worker/Lifecycle/TaskMergeService.cs

@@ -492,7 +492,8 @@ public sealed class TaskMergeService
         CancellationToken ct)
         => MergeAsync(taskId, targetBranch, removeWorktree, commitMessage, leaveConflictsInTree: false, ct);
 
-    public async Task<MergeResult> ContinueMergeAsync(string taskId, CancellationToken ct)
+    public async Task<MergeResult> ContinueMergeAsync(
+        string taskId, CancellationToken ct, IProgress<ProgressNotificationValue>? progress = null)
     {
         var (task, list, wt, verifyCommand) = await LoadMergeContextAsync(taskId, ct);
 
@@ -558,7 +559,7 @@ public sealed class TaskMergeService
             var targetBranch = await _git.GetCurrentBranchAsync(list.WorkingDir, ct);
             await RebaseOthersAfterMergeAsync(task, list, targetBranch, oldTargetTip, mergeSha, ct);
 
-            var verifyFailure = await RunVerifyGateAsync(verifyCommand, list.WorkingDir, ct);
+            var verifyFailure = await RunVerifyGateAsync(verifyCommand, list.WorkingDir, ct, progress);
             if (verifyFailure is not null)
             {
                 _logger.LogWarning("Verify command failed after continuing merge of task {TaskId}: {Reason}", taskId, verifyFailure.ErrorMessage);