feat(ui): warn when the running worker predates the selected repo's merged HEAD

Stamps ClaudeDo.Worker's build with its exact git SHA (SourceRevisionId ->
InformationalVersion) and exposes it via a new GetWorkerBuildInfo hub call.
For the currently selected list, the shell compares that SHA against the
list's git HEAD (GitService.IsAncestorAsync) and shows a persistent footer
banner -- never auto-clearing, never shown on an unrelated repo or when the
ancestry can't be determined -- so "verified against a merge" claims aren't
silently made against a stale process. No auto-restart; the banner just
offers the existing RestartWorkerCommand.

src/ClaudeDo.Ui/Services/Interfaces/IWorkerClient.cs

@@ -130,6 +130,9 @@ public interface IWorkerClient : INotifyPropertyChanged
     Task<string> GetLastPrepLogAsync();
     Task<IReadOnlyList<WorkerLogEntry>> GetRecentLogsAsync();
 
+    /// <summary>Git SHA the running worker was built from (null when offline or the build isn't stamped).</summary>
+    Task<WorkerBuildInfoDto?> GetWorkerBuildInfoAsync();
+
     Task<List<PrimeScheduleDto>> GetPrimeSchedulesAsync();
     Task<PrimeScheduleDto?> UpsertPrimeScheduleAsync(PrimeScheduleDto dto);
     Task DeletePrimeScheduleAsync(Guid id);