fix(merge): conventional merge-commit default and live verify progress

The merge commit message was hand-rolled per caller ("Merge task: <title>",
"Merge <branch>", "Merge subtask") and ignored the task's commit type. Every
caller now passes a blank message and TaskMergeService fills in
CommitMessageBuilder.BuildMerge -> {commitType}(list-slug): merge <title> plus the
ClaudeDo-Task trailer; the merge modal prefills it from GetMergeTargets.

A merge whose list has a verify command holds the MergeTask call for minutes (5m46s
on this repo), during which the modal only disabled its button - no spinner, no
message, so a landed merge looked like a dead app. TaskMergeService now broadcasts
MergeProgress(taskId, phase, elapsedSeconds) for the merging and verifying phases
(re-reported every 30s) plus a WorkerLog line when verify starts; the modal shows a
spinner and the localized phase.

src/ClaudeDo.Worker/Hub/HubBroadcaster.cs

@@ -46,6 +46,11 @@ public sealed class HubBroadcaster : IPrimeBroadcaster, IRefineBroadcaster
     public Task WorkerLog(string message, WorkerLogLevel level, DateTime timestampUtc) =>
         _hub.Clients.All.SendAsync("WorkerLog", message, level, timestampUtc);
 
+    // Phase of an in-flight single-task merge (see TaskMergeService.Phase*), so a client waiting
+    // on the MergeTask call can show what it is waiting for instead of a frozen button.
+    public Task MergeProgress(string taskId, string phase, int elapsedSeconds) =>
+        _hub.Clients.All.SendAsync("MergeProgress", taskId, phase, elapsedSeconds);
+
     public Task PlanningMergeStarted(string planningTaskId, string targetBranch) =>
         _hub.Clients.All.SendAsync("PlanningMergeStarted", planningTaskId, targetBranch);
 

src/ClaudeDo.Worker/Hub/WorkerHub.cs

@@ -96,7 +96,8 @@ public record SetTaskStatusResultDto(BaseDirtyWarningDto? BaseDirty);
 public record MergePreviewDto(
     string Status, IReadOnlyList<string> ConflictFiles, int ChangedFileCount,
     int? VerifyExitCode = null, long? VerifyDurationMs = null, string? VerifyOutputTail = null);
-public record MergeTargetsDto(string DefaultBranch, IReadOnlyList<string> LocalBranches);
+public record MergeTargetsDto(
+    string DefaultBranch, IReadOnlyList<string> LocalBranches, string DefaultCommitMessage);
 public record MergeConflictDocumentsDto(string TaskId, IReadOnlyList<ConflictDocumentDto> Files);
 public record ConflictDocumentDto(string Path, bool IsBinary, IReadOnlyList<MergeSegmentDto> Segments);
 public record MergeSegmentDto(bool IsConflict, string Text, string Ours, string? Base, string Theirs);
@@ -588,11 +589,13 @@ public sealed class WorkerHub : Microsoft.AspNetCore.SignalR.Hub
         string taskId, string targetBranch, bool removeWorktree, string commitMessage)
         => HubGuard(async () =>
         {
+            // A blank message is handed through deliberately — TaskMergeService builds the
+            // conventional default from the task's commit type and its list's name.
             var r = await _mergeService.MergeAsync(
                 taskId,
                 targetBranch ?? "",
                 removeWorktree,
-                string.IsNullOrWhiteSpace(commitMessage) ? "Merge task" : commitMessage,
+                commitMessage,
                 CancellationToken.None);
             return new MergeResultDto(r.Status, r.ConflictFiles, r.ErrorMessage);
         });
@@ -601,7 +604,7 @@ public sealed class WorkerHub : Microsoft.AspNetCore.SignalR.Hub
         => HubGuard(async () =>
         {
             var t = await _mergeService.GetTargetsAsync(taskId, CancellationToken.None);
-            return new MergeTargetsDto(t.DefaultBranch, t.LocalBranches);
+            return new MergeTargetsDto(t.DefaultBranch, t.LocalBranches, t.DefaultCommitMessage);
         });
 
     public Task<MergePreviewDto> PreviewMerge(string taskId, string targetBranch)
@@ -615,7 +618,7 @@ public sealed class WorkerHub : Microsoft.AspNetCore.SignalR.Hub
         => HubGuard(async () =>
         {
             var r = await _mergeService.MergeAsync(
-                taskId, targetBranch ?? "", removeWorktree: false, "Merge task",
+                taskId, targetBranch ?? "", removeWorktree: false, commitMessage: "",
                 leaveConflictsInTree: true, CancellationToken.None);
             if (r.Status == TaskMergeService.StatusBlocked)
                 throw new HubException(r.ErrorMessage ?? "merge blocked");