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/TasksIslandRegroupTests.cs

@@ -64,6 +64,7 @@ public class TasksIslandRegroupTests : IDisposable
 
         db.Tasks.Add(new TaskEntity
         {
+            Number = TestTaskNumbers.Next(),
             Id = parentId,
             ListId = list.Id,
             Title = "Parent",
@@ -74,6 +75,7 @@ public class TasksIslandRegroupTests : IDisposable
         });
         db.Tasks.Add(new TaskEntity
         {
+            Number = TestTaskNumbers.Next(),
             Id = childId,
             ListId = list.Id,
             Title = "Child",
@@ -116,6 +118,7 @@ public class TasksIslandRegroupTests : IDisposable
         {
             db.Tasks.Add(new TaskEntity
             {
+                Number = TestTaskNumbers.Next(),
                 Id = t.Id,
                 ListId = "list1",
                 Title = t.Id,