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/WorkerClient.cs

@@ -423,6 +423,9 @@ public partial class WorkerClient : ObservableObject, IAsyncDisposable, IWorkerC
     public async Task<string> GetLastPrepLogAsync()
         => await TryInvokeAsync<string>("GetLastPrepLog") ?? string.Empty;
 
+    public Task<WorkerBuildInfoDto?> GetWorkerBuildInfoAsync()
+        => TryInvokeAsync<WorkerBuildInfoDto>("GetWorkerBuildInfo");
+
     public async Task<IReadOnlyList<WorkerLogEntry>> GetRecentLogsAsync()
         => await TryInvokeAsync<List<WorkerLogEntry>>("GetRecentLogs") ?? new List<WorkerLogEntry>();
 
@@ -687,6 +690,7 @@ public sealed record LaunchSpec(
 
 public sealed record ForceRemoveResultDto(bool Removed, string? Reason);
 public sealed record PendingQuestionDto(string TaskId, string QuestionId, string Question);
+public sealed record WorkerBuildInfoDto(string? BuildSha);
 
 public sealed record OnlineInboxStateDto(
     bool Enabled,