fix: default task deadline to date only

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

@@ -63,9 +63,9 @@ describe('task utilities', () => {
     expect(filterTasks(searchable, '工作').map((task) => task.id)).toEqual(['4'])
   })
 
-  it('defaults new tasks to today at noon in local time', () => {
+  it('defaults new tasks to today without a time', () => {
     const due = defaultTaskDueAt(new Date(2026, 8, 8, 21, 30))
-    expect(due).toBe('2026-09-08T12:00')
+    expect(due).toBe('2026-09-08')
   })
 
   it('formats API dates in local wall-clock time', () => {

frontend/src/lib/task-utils.ts

@@ -148,7 +148,7 @@ export function defaultTaskDueAt(now = new Date()) {
   const year = now.getFullYear()
   const month = `${now.getMonth() + 1}`.padStart(2, '0')
   const day = `${now.getDate()}`.padStart(2, '0')
-  return `${year}-${month}-${day}T12:00`
+  return `${year}-${month}-${day}`
 }
 
 export function toDateTimeLocal(value: string | null | undefined) {