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.

tests/ClaudeDo.Worker.Tests/Hub/WorkerBuildInfoHubTests.cs

@@ -0,0 +1,36 @@
+using ClaudeDo.Worker.Hub;
+using Xunit;
+
+namespace ClaudeDo.Worker.Tests.Hub;
+
+public sealed class WorkerBuildInfoHubTests
+{
+    [Theory]
+    [InlineData(null, null)]
+    [InlineData("", null)]
+    [InlineData("1.2.3", null)]
+    [InlineData("1.2.3+", null)]
+    [InlineData("1.2.3+abc1234", "abc1234")]
+    // MinVer's own pre-release metadata can already contain a '+' (e.g. "+devsha"); our
+    // SourceRevisionId is appended last, so only the segment after the LAST '+' is authoritative.
+    [InlineData("0.0.0-alpha.0.4+devsha+f5b1a2c3d4e5f6a7b8c9d0e1f2a3b4c5d6e7f8a9", "f5b1a2c3d4e5f6a7b8c9d0e1f2a3b4c5d6e7f8a9")]
+    public void ParseBuildSha_ExtractsSegmentAfterLastPlus(string? informationalVersion, string? expected)
+    {
+        Assert.Equal(expected, WorkerHub.ParseBuildSha(informationalVersion));
+    }
+
+    [Fact]
+    public void GetWorkerBuildInfo_ReturnsDto()
+    {
+        var hub = new WorkerHub(
+            null!, null!, null!, null!, null!, null!,
+            null!, null!, null!, null!, null!, null!, null!, null!, null!, null!, null!, null!, null!,
+            null!, new ClaudeDo.Worker.Online.OnlineInboxConfig(), new ClaudeDo.Worker.Online.OnlineTokenStore(),
+            new ClaudeDo.Worker.Runner.PendingQuestionRegistry(), null!);
+
+        // No assertion on the actual SHA value (depends on the build environment) — just that
+        // the call doesn't throw and always returns a DTO, never null.
+        var info = hub.GetWorkerBuildInfo();
+        Assert.NotNull(info);
+    }
+}