fix(test): give Ui.Tests task seeds a unique Number

The task-numbers slice added a UNIQUE index on tasks.number. Ui.Tests seed
TaskEntity rows directly instead of going through TaskRepository, so every row
kept the default Number = 0 and 31 tests failed with
'UNIQUE constraint failed: tasks.number'.

tests/ClaudeDo.Ui.Tests/ViewModels/TasksIslandSelectByIdTests.cs

@@ -50,6 +50,7 @@ public class TasksIslandSelectByIdTests : IDisposable
         });
         db.Tasks.Add(new TaskEntity
         {
+            Number = TestTaskNumbers.Next(),
             Id = "T1",
             ListId = "L1",
             Title = "My task",