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/Services/VerifyCommandRunnerTests.cs

@@ -0,0 +1,60 @@
+using ClaudeDo.Worker.Lifecycle;
+
+namespace ClaudeDo.Worker.Tests.Services;
+
+public class VerifyCommandRunnerTests
+{
+    private readonly VerifyCommandRunner _runner = new();
+
+    [Fact]
+    public async Task RunAsync_ExitsZero_ReportsSuccessNotTimedOut()
+    {
+        var result = await _runner.RunAsync(
+            Path.GetTempPath(), "exit 0", TimeSpan.FromSeconds(30), CancellationToken.None);
+
+        Assert.Equal(0, result.ExitCode);
+        Assert.False(result.TimedOut);
+    }
+
+    [Fact]
+    public async Task RunAsync_NonZeroExit_ReportsExitCode()
+    {
+        var result = await _runner.RunAsync(
+            Path.GetTempPath(), "exit 7", TimeSpan.FromSeconds(30), CancellationToken.None);
+
+        Assert.Equal(7, result.ExitCode);
+        Assert.False(result.TimedOut);
+    }
+
+    [Fact]
+    public async Task RunAsync_CapturesStdoutAndStderr()
+    {
+        var result = await _runner.RunAsync(
+            Path.GetTempPath(), "echo hello-out & echo hello-err 1>&2", TimeSpan.FromSeconds(30), CancellationToken.None);
+
+        Assert.Contains("hello-out", result.Output);
+        Assert.Contains("hello-err", result.Output);
+    }
+
+    [Fact]
+    public async Task RunAsync_RunsInSpecifiedWorkingDirectory()
+    {
+        var dir = Path.Combine(Path.GetTempPath(), $"verify_wd_{Guid.NewGuid():N}");
+        Directory.CreateDirectory(dir);
+        try
+        {
+            var result = await _runner.RunAsync(dir, "cd", TimeSpan.FromSeconds(30), CancellationToken.None);
+            Assert.Contains(new DirectoryInfo(dir).Name, result.Output);
+        }
+        finally { Directory.Delete(dir, recursive: true); }
+    }
+
+    [Fact]
+    public async Task RunAsync_ExceedsTimeout_KillsProcessAndReportsTimedOut()
+    {
+        var result = await _runner.RunAsync(
+            Path.GetTempPath(), "ping -n 60 127.0.0.1", TimeSpan.FromMilliseconds(300), CancellationToken.None);
+
+        Assert.True(result.TimedOut);
+    }
+}