fix(data): merge preflights ignore untracked files in target working tree

HasChangesAsync counted untracked files, so a stray file in the shared
target working dir (e.g. left by a concurrent session) blocked merge
preflights even though nothing tracked changed. Add an includeUntracked
overload defaulting to true, and pass includeUntracked: false only from
the two target-working-tree merge preflights (TaskMergeService.MergeAsync,
PlanningMergeOrchestrator.StartAsync). Auto-commit and the worktree
cleanup data-loss guard keep counting untracked files, since those
callers need to know about them.

src/ClaudeDo.Worker/Lifecycle/TaskMergeService.cs

@@ -115,7 +115,7 @@ public sealed class TaskMergeService
             return Blocked("working directory is not a git repository");
         if (await _git.IsMidMergeAsync(list.WorkingDir, ct))
             return Blocked("target working directory is mid-merge");
-        if (await _git.HasChangesAsync(list.WorkingDir, ct))
+        if (await _git.HasChangesAsync(list.WorkingDir, includeUntracked: false, ct))
             return Blocked("target working tree has uncommitted changes");
 
         var currentBranch = await _git.GetCurrentBranchAsync(list.WorkingDir, ct);

src/ClaudeDo.Worker/Planning/PlanningMergeOrchestrator.cs

@@ -87,7 +87,7 @@ public sealed class PlanningMergeOrchestrator
         if (await _git.IsMidMergeAsync(workingDir, ct))
             throw new InvalidOperationException(
                 "repo is mid-merge; use AbortPlanningMerge to reset the repository, then Approve again");
-        if (await _git.HasChangesAsync(workingDir, ct))
+        if (await _git.HasChangesAsync(workingDir, includeUntracked: false, ct))
             throw new InvalidOperationException("working tree has uncommitted changes");
 
         var idsToMerge = new List<string>();