feat(schemas): 更新 Pydantic Schema，新增请求/响应模型

Task Schema 更新:
- TaskResponse/TaskSummaryResponse 新增 is_rework, reject_reason, received_at, completed_at 字段
- 新增 TaskRejectRequest (品质驳回请求, reason 必填)
- 新增 TaskTransferRequest (裂变转交请求, next_assignees + next_task_name 必填)
- 新增 TaskTransferResponse (裂变转交响应)
- TaskCreate 新增 is_rework 字段

Product Schema 更新:
- ProductResponse/ProductScanResponse 新增 current_location_id 字段
- ProductScanResponse 新增 task_tree 字段 (递归任务树，供十字矩阵树状图)

backend/app/schemas/task.py

@@ -0,0 +1,120 @@
+"""任务 Pydantic Schemas — 支持无限嵌套子任务、裂变转交、驳回返工"""
+from __future__ import annotations
+import uuid
+from datetime import datetime
+from typing import Optional
+from pydantic import BaseModel, Field
+
+
+# ============================================================
+# 请求模型
+# ============================================================
+
+class TaskCreate(BaseModel):
+    """创建任务"""
+    product_id: uuid.UUID = Field(..., description="所属产品ID")
+    parent_task_id: uuid.UUID | None = Field(None, description="父任务ID(用于嵌套子任务/裂变分支)")
+    task_name: str = Field(..., max_length=200, description="任务名称")
+    assignee_id: str | None = Field(None, max_length=64, description="负责人ID(逻辑外键→老系统)")
+    notify_parent_on_complete: bool = Field(False, description="完成后是否通知父任务")
+    is_rework: bool = Field(False, description="是否为返工任务")
+
+    model_config = {"from_attributes": True}
+
+
+class TaskUpdate(BaseModel):
+    """更新任务"""
+    task_name: str | None = Field(None, max_length=200)
+    assignee_id: str | None = Field(None, max_length=64)
+    status: str | None = Field(None, max_length=50, description="任务状态")
+    notify_parent_on_complete: bool | None = Field(None)
+
+    model_config = {"from_attributes": True}
+
+
+class TaskCompleteRequest(BaseModel):
+    """完成任务请求 — 携带转交信息（保留兼容旧版单步转交）"""
+    operator_id: str | None = Field(None, max_length=64, description="操作人ID")
+    next_assignee_id: str | None = Field(None, max_length=64, description="下一步任务负责人ID")
+    next_task_name: str | None = Field(None, max_length=200, description="下一步任务名称")
+    remark: str | None = Field(None, description="完成备注")
+
+
+class SubtaskCreate(BaseModel):
+    """创建子任务"""
+    task_name: str = Field(..., max_length=200, description="子任务名称")
+    assignee_id: str | None = Field(None, max_length=64, description="负责人ID")
+    notify_parent_on_complete: bool = Field(False, description="完成后是否通知父任务")
+
+
+class TaskRejectRequest(BaseModel):
+    """品质驳回请求"""
+    reason: str = Field(..., min_length=1, max_length=500, description="驳回原因（必填）")
+
+
+class TaskTransferRequest(BaseModel):
+    """完工裂变转交请求"""
+    next_assignees: list[str] = Field(..., min_length=1, description="下一道工序接收人列表（必填）")
+    next_task_name: str = Field(..., min_length=1, max_length=200, description="下一道工序名称（必填）")
+    note: str | None = Field(None, description="交接备注")
+
+
+# ============================================================
+# 响应模型
+# ============================================================
+
+class TaskSummaryResponse(BaseModel):
+    """任务摘要 — 扫码时用，不含嵌套子任务"""
+    id: uuid.UUID
+    product_id: uuid.UUID
+    parent_task_id: uuid.UUID | None
+    task_name: str
+    assignee_id: str | None
+    status: str
+    notify_parent_on_complete: bool
+    is_rework: bool = False
+    reject_reason: str | None = None
+    received_at: datetime | None = None
+    completed_at: datetime | None = None
+    created_at: datetime
+
+    model_config = {"from_attributes": True}
+
+
+class TaskResponse(BaseModel):
+    """任务详情响应 — 递归包含所有子任务"""
+    id: uuid.UUID
+    product_id: uuid.UUID
+    parent_task_id: uuid.UUID | None
+    task_name: str
+    assignee_id: str | None
+    status: str
+    notify_parent_on_complete: bool
+    is_rework: bool = False
+    reject_reason: str | None = None
+    received_at: datetime | None = None
+    completed_at: datetime | None = None
+    created_at: datetime
+    child_tasks: list[TaskResponse] = []
+
+    model_config = {"from_attributes": True}
+
+
+class TaskCompleteResponse(BaseModel):
+    """任务完成响应"""
+    completed_task: TaskResponse
+    next_task: TaskResponse | None = None
+    message: str
+
+
+class TaskTransferResponse(BaseModel):
+    """裂变转交响应"""
+    completed_task: TaskResponse
+    created_tasks: list[TaskResponse] = []
+    message: str
+
+
+class TaskListResponse(BaseModel):
+    """任务列表响应"""
+    tasks: list[TaskResponse]
+    total: int