feat: add task and habit reordering

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

@@ -1,5 +1,5 @@
 import { describe, expect, it } from 'vitest'
-import { filterTasks, groupTaskTree, renderMarkdown, toDateTimeLocal } from './task-utils'
+import { filterTasks, groupTaskTree, moveItemWithinScope, renderMarkdown, toDateTimeLocal } from './task-utils'
 
 type SearchTask = {
   id: string
@@ -26,6 +26,18 @@ describe('task utilities', () => {
     expect(groupTaskTree(tasks)).toEqual([{ task: tasks[0], subtasks: [tasks[1]] }, { task: tasks[2], subtasks: [] }])
   })
 
+  it('moves an item before or after another item without changing other scopes', () => {
+    const rows = [
+      { id: 'a', parent_id: null },
+      { id: 'a1', parent_id: 'a' },
+      { id: 'b', parent_id: null },
+      { id: 'c', parent_id: null },
+    ]
+    expect(moveItemWithinScope(rows, 'c', 'a', 'before').map((row) => row.id)).toEqual(['c', 'a1', 'a', 'b'])
+    expect(moveItemWithinScope(rows, 'a', 'c', 'after').map((row) => row.id)).toEqual(['b', 'a1', 'c', 'a'])
+    expect(moveItemWithinScope(rows, 'a1', 'b', 'before')).toEqual(rows)
+  })
+
   it('renders safe basic markdown and strips unsafe html', () => {
     const html = renderMarkdown('# Plan\n**bold** [link](https://example.com)\n<script>alert(1)</script>')
     expect(html).toContain('<h1>Plan</h1>')