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.Worker/ClaudeDo.Worker.csproj

@@ -35,4 +35,18 @@
     <InternalsVisibleTo Include="ClaudeDo.Worker.Tests" />
   </ItemGroup>
 
+  <!-- Stamps this worker's exact commit into AssemblyInformationalVersion as "+{sha}" so a
+       running instance can report which commit it was built from (see WorkerHub.GetWorkerBuildInfo).
+       Independent of MinVer: MinVerVersionOverride (release builds) replaces the base version but
+       doesn't touch SourceRevisionId, and the SDK appends it to InformationalVersion regardless. -->
+  <Target Name="SetBuildRevisionFromGit" BeforeTargets="GetAssemblyVersion" Condition="'$(SourceRevisionId)' == ''">
+    <Exec Command="git rev-parse HEAD"
+          WorkingDirectory="$(MSBuildProjectDirectory)"
+          ConsoleToMSBuild="true"
+          StandardOutputImportance="low"
+          ContinueOnError="WarnAndContinue">
+      <Output TaskParameter="ConsoleOutput" PropertyName="SourceRevisionId" />
+    </Exec>
+  </Target>
+
 </Project>