feat(merge): Stash-Option fuer uncommittete Aenderungen im Ziel-Tree

Ein dirty Ziel-Arbeitsverzeichnis gibt jetzt den eigenen Status
dirty_target zurueck statt blocked. Die UI bietet daraufhin einen
Retry an, der per git merge --autostash stasht, merged und die
Aenderungen danach wiederherstellt - opt-in pro Merge:

- Approve & Merge: Bestaetigungsdialog
- Merge-Modal: Button "Aenderungen stashen und mergen"
- MCP (merge_task/review_task) wirft weiterhin, kein autostash dort

tests/ClaudeDo.Worker.Tests/Services/TaskMergeServiceTests.cs

@@ -392,10 +392,42 @@ public class TaskMergeServiceTests : IDisposable
         var (svc, _) = BuildService(db);
         var result = await svc.MergeAsync(task.Id, "main", false, "Merge", CancellationToken.None);
 
-        Assert.Equal("blocked", result.Status);
+        Assert.Equal(TaskMergeService.StatusDirtyTarget, result.Status);
         Assert.Contains("uncommitted", result.ErrorMessage ?? "");
     }
 
+    [Fact]
+    public async Task MergeAsync_DirtyWorkingTree_WithAutostash_MergesAndRestoresTheChanges()
+    {
+        if (!GitRepoFixture.IsGitAvailable()) return;
+        var repo = NewRepo();
+        var db = NewDb();
+        var (list, task) = await SeedListAndTask(db, workingDir: repo.RepoDir, status: TaskStatus.Done);
+
+        var wtMgr = BuildWorktreeManager(db);
+        var wtCtx = await wtMgr.CreateAsync(task, list, CancellationToken.None);
+        _wtCleanups.Add((repo.RepoDir, wtCtx.WorktreePath));
+
+        // The branch touches a different file than the dirty one, so the stash restores cleanly.
+        File.WriteAllText(Path.Combine(wtCtx.WorktreePath, "feature.txt"), "from the branch\n");
+        GitRepoFixture.RunGit(wtCtx.WorktreePath, "add", "-A");
+        GitRepoFixture.RunGit(wtCtx.WorktreePath, "commit", "-m", "feat: add feature.txt");
+
+        File.WriteAllText(Path.Combine(repo.RepoDir, "README.md"), "dirty\n");
+
+        var currentBranch = await new GitService().GetCurrentBranchAsync(repo.RepoDir);
+        var (svc, _) = BuildService(db);
+        var result = await svc.MergeAsync(
+            task.Id, currentBranch, false, "Merge", leaveConflictsInTree: false, CancellationToken.None,
+            autostash: true);
+
+        Assert.True(result.Status == TaskMergeService.StatusMerged, $"{result.Status}: {result.ErrorMessage}");
+        // The branch landed...
+        Assert.True(File.Exists(Path.Combine(repo.RepoDir, "feature.txt")));
+        // ...and the stashed work is back in the working tree, still uncommitted.
+        Assert.Equal("dirty\n", File.ReadAllText(Path.Combine(repo.RepoDir, "README.md")).Replace("\r\n", "\n"));
+    }
+
     [Fact]
     public async Task MergeAsync_UntrackedFileInTargetWorkingTree_DoesNotBlock()
     {