feat(任务模块): 任务归档 T-ARC-01~08 实现

- 数据: Project.autoArchive + Task.archived/archivedAt/archiveSource,
  迁移 20261026000000_task_archive (两索引)
- 领域: server/task-domain/archive.js —— hiddenAtOf 与保留口径精确同源,
  autoArchiveDue 到期判定, runAutoArchiveForProject (读时惰性) +
  runAutoArchiveSweep (每小时 cron 兜底)
- 接口: POST /tasks/:id/archive|unarchive (连带子任务, 幂等);
  GET /projects/:id/tasks/archived (keyword/kind/columnId/from/to 过滤,
  archivedAt+id 游标分页); 项目 PUT 收 autoArchive (枚举校验);
  主列表/子任务/项目 taskCount 全部排除归档
- 前端: ⋯ 菜单「归档」(确认含子任务条数); 项目栏「已归档」入口 →
  ArchivedTasks 弹层 (关键词/类型/列/归档时段过滤 + 加载更多 + 恢复/删除);
  项目管理「归档设置」四档 Picker

src/api/task.js

@@ -38,4 +38,7 @@ export const taskApi = {
   reorder: (projectId, ids) => api(`/projects/${projectId}/tasks/reorder`, { method: 'POST', body: { ids } }),
   remove: (id) => api(`/tasks/${id}`, { method: 'DELETE' }),
   copy: (id, projectId) => api(`/tasks/${id}/copy`, { method: 'POST', body: { projectId } }),
+  archive: (id) => api(`/tasks/${id}/archive`, { method: 'POST', body: {} }),
+  unarchive: (id) => api(`/tasks/${id}/unarchive`, { method: 'POST', body: {} }),
+  archivedList: (projectId, params) => api(`/projects/${projectId}/tasks/archived` + q(params)),
 }