fix(worker,ui): route details-pane task delete through worker to advance blocked parents

Deleting a child from the details pane hard-deleted straight from the UI
process via TaskRepository, bypassing TaskStateService.TryAdvanceParentAsync
entirely. Deleting the last child of a WaitingForChildren parent that way
left it wedged forever. WorkerHub.DeleteTask now mirrors the MCP delete_task
tool (running-task guard, FK-friendly error, advance-parent call), and the
UI goes through it.

TryAdvanceParentAsync also short-circuited when zero children remained,
treating "no children left" as "nothing to evaluate" instead of "all done" -
removed the early return so an empty child list (vacuously) counts as all
terminal.

src/ClaudeDo.Ui/ViewModels/Islands/DetailsIslandViewModel.cs

@@ -946,18 +946,14 @@ public sealed partial class DetailsIslandViewModel : ViewModelBase, IDisposable
             var ok = await ConfirmAsync($"Delete \"{row.Title}\"? This cannot be undone.");
             if (!ok) return;
         }
-        try
-        {
-            await using var ctx = _dbFactory.CreateDbContext();
-            var repo = new TaskRepository(ctx);
-            await repo.DeleteAsync(row.Id);
-        }
-        catch (Microsoft.EntityFrameworkCore.DbUpdateException ex) when (
-               ex.Message.Contains("FOREIGN KEY", StringComparison.OrdinalIgnoreCase)
-            || ex.InnerException?.Message.Contains("FOREIGN KEY", StringComparison.OrdinalIgnoreCase) == true)
+        // Routed through the worker (mirrors the MCP delete_task tool) so a deleted child
+        // correctly advances a WaitingForChildren parent — a direct-repo delete from here used
+        // to bypass TaskStateService.TryAdvanceParentAsync and could wedge the parent forever.
+        var (deleted, error) = await _worker.DeleteTaskAsync(row.Id);
+        if (!deleted)
         {
             if (ShowErrorAsync != null)
-                await ShowErrorAsync("This task has child tasks. Discard the planning session or delete child tasks first.");
+                await ShowErrorAsync(error ?? "Delete failed.");
             return;
         }
         if (DeleteFromList != null)