fix: align subtask completion control

frontend/src/App.vue

@@ -1536,7 +1536,7 @@ onUnmounted(() => {
           </div>
           <div v-else class="markdown-preview" :class="{'markdown-preview-empty':!selectedTask.description.trim()}" v-html="selectedTask.description.trim() ? renderMarkdown(selectedTask.description) : '<p>暂无备注，切回编辑开始书写。</p>'"/>
         </div>
-        <div class="subtasks"><div class="field-label"><span>子任务</span><button class="link" @click="addSubtask"><Plus/>添加</button></div><div v-for="subtask in selectedTaskSubtasks" :key="subtask.id" class="subtask-detail"><button class="check subtask-check" type="button" :aria-label="subtask.completed ? `重新打开${subtask.title}` : `完成${subtask.title}`" :aria-pressed="subtask.completed" @click="toggle(subtask)"><Check v-if="subtask.completed"/></button><span :class="{strike:subtask.completed}">{{subtask.title}}</span></div><span v-if="!selectedTaskSubtasks.length" class="hint">把这件事拆成更小的步骤</span></div>
+        <div class="subtasks"><div class="field-label"><span>子任务</span><button class="link" @click="addSubtask"><Plus/>添加</button></div><div v-for="subtask in selectedTaskSubtasks" :key="subtask.id" class="subtask-detail"><button class="task-check subtask-check" type="button" :aria-label="subtask.completed ? `重新打开${subtask.title}` : `完成${subtask.title}`" :aria-pressed="subtask.completed" @click="toggle(subtask)"><span class="task-check-mark" :class="`p${subtask.priority}`"><Check v-if="subtask.completed" /></span></button><span :class="{strike:subtask.completed}">{{subtask.title}}</span></div><span v-if="!selectedTaskSubtasks.length" class="hint">把这件事拆成更小的步骤</span></div>
         <details class="more-settings" :open="moreSettingsOpen" @toggle="moreSettingsOpen=($event.target as HTMLDetailsElement).open"><summary>更多设置</summary><div class="more-settings-body">
           <label>优先级<select v-model.number="selectedTask.priority"><option :value="0">无</option><option :value="1">低</option><option :value="2">中</option><option :value="3">高</option></select></label>
         </div></details>

frontend/src/style.test.ts

@@ -610,7 +610,8 @@ describe('task and habit row decoration', () => {
     const subtaskRow = app.slice(app.indexOf('<div v-for="subtask in selectedTaskSubtasks"'), app.indexOf('</div><span v-if="!selectedTaskSubtasks.length"'))
     expect(subtaskRow).toContain('class="subtask-detail"')
     expect(subtaskRow).not.toMatch(/class="subtask-detail"[^>]*@click=/)
-    expect(subtaskRow).toContain('class="check subtask-check"')
+    expect(subtaskRow).toContain('class="task-check subtask-check"')
+    expect(subtaskRow).toContain('<span class="task-check-mark" :class="`p${subtask.priority}`"><Check v-if="subtask.completed" /></span>')
     expect(subtaskRow).toContain('@click="toggle(subtask)"')
     expect(css).toContain('.subtask-detail .subtask-check{width:44px;height:44px;flex:0 0 44px;')
     expect(css).toContain('.task-check{')