feat(board): 支持批量添加与批量删除任务

- 批量添加面板：一行一条，整批共用目标列、优先级、标签与截止日期
- 快速新增支持粘贴多行文本，直接拆成多条任务
- 多选模式支持全选可见任务、整批删除，撤销时连原顺序一起还原
- 批量创建与删除走 store 的批量方法，一次落盘、一次广播
- 补充单元测试与 E2E 用例

src/components/BoardToolbar.vue

@@ -10,9 +10,9 @@ import { isDueToday, isOverdue } from '@/utils/date'
 
 import TagFilter from './TagFilter.vue'
 
-defineProps<{ hiddenNote?: string }>()
+defineProps<{ hiddenNote?: string; selecting?: boolean }>()
 
-const emit = defineEmits<{ archive: [] }>()
+const emit = defineEmits<{ archive: []; 'batch-add': []; 'toggle-select': [] }>()
 
 const store = useTaskStore()
 const filters = useFilterStore()
@@ -133,6 +133,28 @@ defineExpose({ focusSearch })
       <span v-if="hiddenNote" class="text-slate-400 dark:text-zinc-500">{{ hiddenNote }}</span>
 
       <div class="ml-auto flex items-center gap-1.5">
+        <button
+          type="button"
+          class="flex h-8 items-center rounded-md border border-slate-200 bg-white px-2.5 text-xs text-slate-600 transition hover:border-slate-300 hover:bg-slate-50 dark:border-zinc-700 dark:bg-zinc-900 dark:text-zinc-300 dark:hover:border-zinc-600 dark:hover:bg-zinc-800"
+          @click="emit('batch-add')"
+        >
+          批量添加
+        </button>
+
+        <button
+          type="button"
+          class="flex h-8 items-center rounded-md border px-2.5 text-xs transition"
+          :class="
+            selecting
+              ? 'border-sky-300 bg-sky-50 text-sky-700 dark:border-sky-700 dark:bg-sky-950 dark:text-sky-300'
+              : 'border-slate-200 bg-white text-slate-600 hover:border-slate-300 hover:bg-slate-50 dark:border-zinc-700 dark:bg-zinc-900 dark:text-zinc-300 dark:hover:border-zinc-600 dark:hover:bg-zinc-800'
+          "
+          :aria-pressed="selecting === true"
+          @click="emit('toggle-select')"
+        >
+          {{ selecting ? '退出多选' : '多选' }}
+        </button>
+
         <button
           v-if="archivableCount > 0"
           type="button"