feat(worker): add post-merge verification gate for list merges

Per-list optional VerifyCommand (list_config.verify_command) runs via
VerifyCommandRunner in the list's working dir right after a successful
merge/continue-merge, before the task is allowed to reach Done. A
non-zero exit or timeout leaves the merge in place but keeps the task
out of Done and reports StatusVerifyFailed with an output excerpt
through MergeResultDto/review_task; no command configured behaves
exactly as before. Merges against the same repo are now serialized
per working dir so a running verify can't be interrupted by a second
merge landing mid-build. Adds the field to the List Settings modal
(en/de localized) and covers success/failure/timeout in
TaskMergeServiceTests + VerifyCommandRunnerTests.

tests/ClaudeDo.Worker.Tests/Repositories/ListRepositoryConfigTests.cs

@@ -96,6 +96,38 @@ public sealed class ListRepositoryConfigTests : IDisposable
         Assert.Null(fetched.SessionSkills);
     }
 
+    [Fact]
+    public async Task SetConfig_Persists_VerifyCommand_On_Insert()
+    {
+        await _repo.SetConfigAsync(new ListConfigEntity { ListId = _listId, VerifyCommand = "dotnet test" });
+
+        var fetched = await _repo.GetConfigAsync(_listId);
+        Assert.NotNull(fetched);
+        Assert.Equal("dotnet test", fetched.VerifyCommand);
+    }
+
+    [Fact]
+    public async Task SetConfig_Persists_VerifyCommand_On_Update()
+    {
+        await _repo.SetConfigAsync(new ListConfigEntity { ListId = _listId, VerifyCommand = "dotnet build" });
+        await _repo.SetConfigAsync(new ListConfigEntity { ListId = _listId, VerifyCommand = "dotnet test" });
+
+        var fetched = await _repo.GetConfigAsync(_listId);
+        Assert.NotNull(fetched);
+        Assert.Equal("dotnet test", fetched.VerifyCommand);
+    }
+
+    [Fact]
+    public async Task SetConfig_Null_VerifyCommand_Clears_On_Update()
+    {
+        await _repo.SetConfigAsync(new ListConfigEntity { ListId = _listId, VerifyCommand = "dotnet test" });
+        await _repo.SetConfigAsync(new ListConfigEntity { ListId = _listId, VerifyCommand = null });
+
+        var fetched = await _repo.GetConfigAsync(_listId);
+        Assert.NotNull(fetched);
+        Assert.Null(fetched.VerifyCommand);
+    }
+
     public void Dispose()
     {
         _ctx.Dispose();