feat(tasks): 任务列表支持批量修改分类

勾选多个任务后可一次性移动到目标分类,或选「未分类」把它们移出当前分类。

- db: 新增 SetTasksCategory,在单个事务里校验分类存在性并 UPDATE ... WHERE
  id=ANY(...),返回真正被更新的 id 和刷新后的分类(含 task_count)。分类检查
  放在事务内,避免并发删除把 UPDATE 变成外键冲突。单批上限 100。
- server: 新增 POST /api/tasks/category/batch。写入原子,响应里的逐任务失败
  只可能是勾选后又被删掉的任务;顺带把 category_id 的解析(必填但可为 null)
  抽成 parseCategoryIDField 与单任务接口共用。
- server: 把批量 id 的 trim/归一/去重逻辑从 controlTasksBatch 抽成
  normalizeBatchTaskIDs,两个批量端点共用同一套重复判定。
- manager: SetTasksCategory 在 taskStateMu 内完成 DB 写入与运行中任务 DTO
  刷新,防止与单任务更新交错后留下过期的 category_name。
- web: 选中工具栏新增「修改分类」对话框(需确认目标,避免误点批量改动);
  「未分类」哨兵值统一提取为 UNCATEGORIZED_VALUE。

验证: go build / vet / gofmt、db 与 server 新增测试连本地 PG 实跑通过、
tsc --noEmit、biome check、next build 均通过。

db/task_categories.go

@@ -13,6 +13,10 @@ import (
 
 const MaxTaskCategoryNameRunes = 80
 
+// MaxTaskCategoryBatchSize bounds one batch move so a single request cannot lock
+// an unbounded number of task rows.
+const MaxTaskCategoryBatchSize = 100
+
 var (
 	ErrTaskCategoryInvalid      = errors.New("invalid task category")
 	ErrTaskCategoryNameConflict = errors.New("task category name already exists")
@@ -199,3 +203,80 @@ FROM selected, updated`, taskID, *categoryID))
 	}
 	return &category, nil
 }
+
+// SetTasksCategory moves several tasks into one category (nil = uncategorized)
+// inside a single transaction, so a half-applied batch is never observable.
+// It returns the ids that were actually updated — ids missing from that slice
+// were deleted between selection and submit — plus the refreshed category row
+// whose task_count already reflects this move.
+func (d *DB) SetTasksCategory(taskIDs []int64, categoryID *int64) ([]int64, *TaskCategory, error) {
+	if len(taskIDs) == 0 {
+		return nil, nil, fmt.Errorf("%w: task ids are required", ErrTaskCategoryInvalid)
+	}
+	if len(taskIDs) > MaxTaskCategoryBatchSize {
+		return nil, nil, fmt.Errorf("%w: at most %d tasks per request", ErrTaskCategoryInvalid, MaxTaskCategoryBatchSize)
+	}
+	for _, id := range taskIDs {
+		if id <= 0 {
+			return nil, nil, fmt.Errorf("%w: task id must be positive", ErrTaskCategoryInvalid)
+		}
+	}
+	if categoryID != nil && *categoryID <= 0 {
+		return nil, nil, fmt.Errorf("%w: category id must be positive", ErrTaskCategoryInvalid)
+	}
+	tx, err := d.Begin()
+	if err != nil {
+		return nil, nil, err
+	}
+	defer tx.Rollback() //nolint:errcheck
+
+	// Checking the category inside the transaction keeps a concurrent delete from
+	// turning the UPDATE below into a foreign key violation.
+	if categoryID != nil {
+		var exists bool
+		if err := tx.QueryRow(`SELECT EXISTS(SELECT 1 FROM task_categories WHERE id=$1)`, *categoryID).Scan(&exists); err != nil {
+			return nil, nil, err
+		}
+		if !exists {
+			return nil, nil, ErrTaskCategoryNotFound
+		}
+	}
+	rows, err := tx.Query(`
+UPDATE tasks SET category_id=$2
+WHERE id=ANY($1::bigint[]) AND deleted_at IS NULL
+RETURNING id`, taskIDs, categoryID)
+	if err != nil {
+		return nil, nil, err
+	}
+	updated := make([]int64, 0, len(taskIDs))
+	for rows.Next() {
+		var id int64
+		if err := rows.Scan(&id); err != nil {
+			rows.Close()
+			return nil, nil, err
+		}
+		updated = append(updated, id)
+	}
+	rows.Close()
+	if err := rows.Err(); err != nil {
+		return nil, nil, err
+	}
+
+	var category *TaskCategory
+	if categoryID != nil {
+		fetched, err := scanTaskCategory(tx.QueryRow(`
+SELECT `+taskCategoryCols+`
+FROM task_categories category
+LEFT JOIN tasks task ON task.category_id=category.id
+WHERE category.id=$1
+GROUP BY category.id`, *categoryID))
+		if err != nil {
+			return nil, nil, err
+		}
+		category = &fetched
+	}
+	if err := tx.Commit(); err != nil {
+		return nil, nil, err
+	}
+	return updated, category, nil
+}