feat(V0.2): 任务模块 —— 项目 / 列表与看板 / 列-状态绑定 / 一级子任务

需求 142 条 (T-*), 设计见 docs/V0.2/任务模块/

数据层:
- 新增 6 张表: Project / ProjectMember / BoardColumn / Task / TaskMember / TaskTag
- 看板列是实体(可增删改排序), Task.columnId 外键 RESTRICT 防误删列丢任务
- Task.status(todo/doing/done) 与 columnId 双落库, 二者正交

领域层 server/task-domain/ (唯一口径, 前后端不重复实现):
- resolveStatus: 列决定状态(只看目标列, 无拖出回退); 状态与列不匹配时按列序取第一个绑定该状态的列自动归位, 无匹配列则不移动; 子任务完全豁免
- retention: 逐列 6 档保留窗口(永不显示/当天/3天/本周/本月/永久显示), 以 doneAt 判定
- copyTask: 跨项目深拷贝, 人员按目标项目成员过滤并回报丢弃名单

接口: /api/projects, /api/columns, /api/tasks (均校验项目成员)

前端:
- 底部 Tab 插入「任务」, 位于「打卡」之后; 默认首页仍为打卡
- 列表视图(子任务缩进+折叠) / 看板视图(长按拖拽换列、拖到卡片降为子任务)
- 列设置(列管理+状态绑定+保留选项) / 任务详情(扩展信息卡片默认收起) / 成员管理
- 视图记忆与上次项目存设备端

已验证: 95 文件语法 0 错误、相对导入 0 缺失、领域逻辑用例全部通过

prisma/schema.prisma

@@ -25,6 +25,13 @@ model User {
   checkIns   CheckIn[]
   checkLists CheckList[]
   templates  CheckListTemplate[]
+
+  // V0.2 任务模块
+  ownedProjects  Project[]       @relation("ProjectOwner")
+  projectMembers ProjectMember[]
+  assignedTasks  Task[]          @relation("TaskAssignee")
+  createdTasks   Task[]          @relation("TaskCreator")
+  taskMembers    TaskMember[]
 }
 
 model Article {
@@ -373,5 +380,109 @@ model CheckListTemplate {
 
   @@index([userId, builtin])
 }
+
+// ================== 任务模块 (V0.2 任务模块需求文档 T-*) ==================
+// 口径见 docs/V0.2/任务模块/任务模块数据库设计文档.md
+//   项目 = 隔离 + 权限单位; 看板列是实体(可增删改排序);
+//   任务状态(todo/doing/done) 与 看板列 是两个正交维度, 由列的 boundStatus 决定是否联动.
 
+model Project {
+  id         Int      @id @default(autoincrement())
+  name       String   @db.VarChar(50)
+  ownerId    Int
+  owner      User     @relation("ProjectOwner", fields: [ownerId], references: [id], onDelete: Cascade)
+  isPersonal Boolean  @default(false)
+  archived   Boolean  @default(false)
+  createdAt  DateTime @default(now())
+  updatedAt  DateTime @updatedAt
 
+  members ProjectMember[]
+  columns BoardColumn[]
+  tasks   Task[]
+
+  @@index([ownerId])
+  @@index([archived])
+}
+
+model ProjectMember {
+  id         Int      @id @default(autoincrement())
+  projectId  Int
+  project    Project  @relation(fields: [projectId], references: [id], onDelete: Cascade)
+  userId     Int
+  user       User     @relation(fields: [userId], references: [id], onDelete: Cascade)
+  permission String   @default("member")
+  createdAt  DateTime @default(now())
+
+  @@unique([projectId, userId])
+  @@index([userId])
+}
+
+model BoardColumn {
+  id          Int      @id @default(autoincrement())
+  projectId   Int
+  project     Project  @relation(fields: [projectId], references: [id], onDelete: Cascade)
+  name        String   @db.VarChar(20)
+  sortOrder   Int      @default(0)
+  boundStatus String?  @db.VarChar(8)
+  retention   String   @default("forever") @db.VarChar(8)
+  createdAt   DateTime @default(now())
+  updatedAt   DateTime @updatedAt
+
+  tasks Task[]
+
+  @@unique([projectId, name])
+  @@index([projectId, sortOrder])
+}
+
+model Task {
+  id          Int       @id @default(autoincrement())
+  projectId   Int
+  project     Project   @relation(fields: [projectId], references: [id], onDelete: Cascade)
+  columnId    Int
+  column      BoardColumn @relation(fields: [columnId], references: [id], onDelete: Restrict)
+  parentId    Int?
+  parent      Task?     @relation("Subtask", fields: [parentId], references: [id], onDelete: Cascade)
+  children    Task[]    @relation("Subtask")
+
+  title       String    @db.VarChar(200)
+  description String    @default("") @db.Text
+  status      String    @default("todo") @db.VarChar(8)
+  doneAt      DateTime?
+
+  assigneeId  Int?
+  assignee    User?     @relation("TaskAssignee", fields: [assigneeId], references: [id], onDelete: SetNull)
+  creatorId   Int
+  creator     User      @relation("TaskCreator", fields: [creatorId], references: [id], onDelete: Cascade)
+
+  extras      Json      @default("[]")
+  sortOrder   Int       @default(0)
+  createdAt   DateTime  @default(now())
+  updatedAt   DateTime  @updatedAt
+
+  members TaskMember[]
+  tags    TaskTag[]
+
+  @@index([projectId, columnId])
+  @@index([projectId, status])
+  @@index([parentId])
+  @@index([projectId, doneAt])
+}
+
+model TaskMember {
+  id     Int  @id @default(autoincrement())
+  taskId Int
+  task   Task @relation(fields: [taskId], references: [id], onDelete: Cascade)
+  userId Int
+  user   User @relation(fields: [userId], references: [id], onDelete: Cascade)
+
+  @@unique([taskId, userId])
+}
+
+model TaskTag {
+  id     Int    @id @default(autoincrement())
+  taskId Int
+  task   Task   @relation(fields: [taskId], references: [id], onDelete: Cascade)
+  name   String @db.VarChar(20)
+
+  @@index([taskId])
+}