refactor(worker): extract ProgressReporter from TaskMergeService

Pulls the MCP idle-timeout progress loop out of TaskMergeService into a
standalone ProgressReporter (Lifecycle namespace) shared by the verify
gate and preview-verify call sites, and adds a per-item i/n overload
(ReportItem) for upcoming batch progress in D2/D3.

src/ClaudeDo.Worker/Lifecycle/ProgressReporter.cs

@@ -0,0 +1,47 @@
+using ModelContextProtocol;
+
+namespace ClaudeDo.Worker.Lifecycle;
+
+/// <summary>
+/// Reports MCP/hub progress for a long-running operation so a waiting caller doesn't hit an
+/// idle-silence abort (Claude Code's MCP client aborts an MCP call after ~300s of silence).
+/// </summary>
+internal static class ProgressReporter
+{
+    /// <summary>
+    /// Awaits <paramref name="work"/> while reporting progress every <paramref name="interval"/>.
+    /// <paramref name="onTick"/> rides the same cadence for non-MCP callers (e.g. the Hub, which
+    /// turns it into an OperationProgress broadcast). No-op passthrough when both are null.
+    /// </summary>
+    public static async Task<T> RunAsync<T>(
+        Task<T> work, TimeSpan interval, IProgress<ProgressNotificationValue>? progress, string message,
+        Action<TimeSpan>? onTick = null)
+    {
+        if (progress is null && onTick is null) return await work;
+
+        var sw = System.Diagnostics.Stopwatch.StartNew();
+        while (true)
+        {
+            var finished = await Task.WhenAny(work, Task.Delay(interval));
+            if (finished == work) return await work;
+            progress?.Report(new ProgressNotificationValue { Progress = 0, Message = $"{message} ({sw.Elapsed:mm\\:ss})" });
+            onTick?.Invoke(sw.Elapsed);
+        }
+    }
+
+    /// <summary>
+    /// Reports progress for one processed item out of a known total, e.g. "cleaning worktrees
+    /// (3/12)". For callers iterating a batch (cleanup_task_worktree, get_task_diff,
+    /// preview_merge_set) instead of awaiting one long-running task.
+    /// </summary>
+    public static void ReportItem(
+        IProgress<ProgressNotificationValue>? progress, string action, int current, int total)
+    {
+        progress?.Report(new ProgressNotificationValue
+        {
+            Progress = current,
+            Total = total,
+            Message = $"{action} ({current}/{total})",
+        });
+    }
+}