feat: collapse subtasks from parent rows

frontend/src/lib/task-utils.test.ts

@@ -8,6 +8,7 @@ type SearchTask = {
   parent_id?: string | null
   completed?: boolean
   list_name?: string
+  subtasks?: SearchTask[]
 }
 
 const tasks: SearchTask[] = [
@@ -26,6 +27,12 @@ describe('task utilities', () => {
     expect(groupTaskTree(tasks)).toEqual([{ task: tasks[0], subtasks: [tasks[1]] }, { task: tasks[2], subtasks: [] }])
   })
 
+  it('preserves subtasks already nested by the task API', () => {
+    const child: SearchTask = { id: 'nested-child', title: 'Nested child', parent_id: 'nested-parent' }
+    const parent: SearchTask = { id: 'nested-parent', title: 'Nested parent', parent_id: null, subtasks: [child] }
+    expect(groupTaskTree([parent])).toEqual([{ task: parent, subtasks: [child] }])
+  })
+
   it('moves an item before or after another item without changing other scopes', () => {
     const rows = [
       { id: 'a', parent_id: null },