feat(ui): surface depends_on blocking in status chip, chain label, and detail pane

Usability-Audit 2026-09-10 found three gaps versus the dependency-chain-display
spec: a Queued task blocked on an unmet task_dependencies edge rendered the same
chip as one about to run, a cross-list predecessor silently dropped the
"after #N" chip, and the detail pane showed nothing about a wait at all.

- TaskRowViewModel gains IsBlockedByDependency/DependencyWaitLabel (extrinsic,
  assigned by TasksIslandViewModel like the existing chain fields); IsQueued/
  IsWaiting/StatusChipClass/StatusLabel/StatusChipTooltip now account for it
  alongside the existing BlockedByTaskId planning-chain link.
- TasksIslandViewModel.ApplyDependencyWaitState computes the blocked flag and
  wait label per row; a new RefreshExternalDependencyCacheAsync backfills
  Number/Title/Status for predecessors not loaded into the current list's
  Items (reusing the already-open DbContext, no new hub method), so
  BuildAfterLabel/blocking both resolve a listenfremder Vorgänger correctly.
- New "waiting" chip style (IslandStyles.axaml) and locale keys (en+de);
  TaskHeaderBar shows a "Waiting on #N" line bound straight to the same row.

Tests: TasksIslandChainTests (blocked/unblocked chip, cross-list predecessor),
DetailsIslandDependencyWaitTests (new), TaskRowViewModelNotificationsTests
updated for the new notification set.

tests/ClaudeDo.Worker.Tests/UiVm/TaskRowViewModelNotificationsTests.cs

@@ -281,10 +281,41 @@ public class TaskRowViewModelNotificationsTests
             nameof(TaskRowViewModel.IsQueued),
             nameof(TaskRowViewModel.IsWaiting),
             nameof(TaskRowViewModel.StatusChipClass),
+            nameof(TaskRowViewModel.StatusLabel),
+            nameof(TaskRowViewModel.StatusChipTooltip),
             nameof(TaskRowViewModel.CanRemoveFromQueue),
         }, raised);
     }
 
+    [Fact]
+    public void IsBlockedByDependencyChanged_Notifies_Dependents()
+    {
+        var vm = new TaskRowViewModel { Id = "t" };
+        var raised = Raised(vm, () => vm.IsBlockedByDependency = true);
+        Assert.Equal(new HashSet<string?>
+        {
+            nameof(TaskRowViewModel.IsBlockedByDependency),
+            nameof(TaskRowViewModel.IsQueued),
+            nameof(TaskRowViewModel.IsWaiting),
+            nameof(TaskRowViewModel.StatusChipClass),
+            nameof(TaskRowViewModel.StatusLabel),
+            nameof(TaskRowViewModel.StatusChipTooltip),
+            nameof(TaskRowViewModel.CanRemoveFromQueue),
+        }, raised);
+    }
+
+    [Fact]
+    public void DependencyWaitLabelChanged_Notifies_Dependents()
+    {
+        var vm = new TaskRowViewModel { Id = "t" };
+        var raised = Raised(vm, () => vm.DependencyWaitLabel = "#42");
+        Assert.Equal(new HashSet<string?>
+        {
+            nameof(TaskRowViewModel.DependencyWaitLabel),
+            nameof(TaskRowViewModel.StatusChipTooltip),
+        }, raised);
+    }
+
     [Fact]
     public void HasPlanningChildrenChanged_Notifies_Dependents()
     {