feat(task): 任务中心扫码接单(多端) —— 服务端任务状态机/端口/迁移

- Task 加 task_code/tags/display_priority/claimed_by/claimed_at/doing_at；新增 TaskClaim 流水表。
- TaskService 加 claimed/doing/completed 状态机(claim/start_doing/complete)，grab 并入 claim。
- TaskRepository 加 list_published/get_by_code/update/claim/set_doing + TaskClaimRepository；挂 Database。
- 端口：
  · opc  /tasks/grab-by-code、/tasks/{id}/doing、/tasks/{id}/complete
  · operator POST /tasks(auto task_code) + PATCH /tasks/:id
  · park  /park/api/tasks(大屏展示,含 scan_payload 二维码载荷)
  · training /api/tasks/claim-by-code、/api/tasks/my(小程序 C 端账号→OPC 身份 find-or-create 领单)
- 迁移 0008(tasks 加列 + task_claims)已应用+stamp；seed 补 task_code/tags/grab demo。
- tests/test_task_claim.py(自包含内存库, 状态机+流水+list_published), 直接 async 校验通过。

Co-Authored-By: Claude <noreply@anthropic.com>

app/infrastructure/models.py

@@ -196,26 +196,57 @@ class Agent(Base):
 # ── 运营端业务模型（平台运营/任务/服务商/内容/配置）────────────────────────
 
 class Task(Base):
-    """平台任务（运营端可审核/下架；后续各端口接入）。"""
+    """平台任务（运营端可审核/下架；后续各端口接入）。
+
+    状态机（扩展支持扫码接单）：draft/pending/review/published/claimed/doing/completed/cancelled。
+    扫码接单流转：published → claimed(claimed_by/claimed_at) → doing(doing_at) → completed。
+    历史接单流水见 TaskClaim；claim 记录 claimed_by/claimed_at/doing_at。
+    """
 
     __tablename__ = "tasks"
 
     id: Mapped[str] = mapped_column(String, primary_key=True)
+    task_code: Mapped[str] = mapped_column(String, default="", index=True)  # 展示/扫码短码(唯一)
     title: Mapped[str] = mapped_column(String, default="")
     category: Mapped[str] = mapped_column(String, default="")   # 设计创意/技术开发/...
     sub_category: Mapped[str] = mapped_column(String, default="")
     description: Mapped[str] = mapped_column(Text, default="")
+    tags: Mapped[str] = mapped_column(String, default="")   # 逗号分隔展示标签
     mode: Mapped[str] = mapped_column(String, default="grab")   # grab/bid/designated/dispatch
     budget_min: Mapped[int] = mapped_column(Integer, default=0)
     budget_max: Mapped[int] = mapped_column(Integer, default=0)
     deadline: Mapped[str] = mapped_column(String, default="")
-    status: Mapped[str] = mapped_column(String, default="draft")  # draft/pending/review/published/completed/cancelled
+    display_priority: Mapped[int] = mapped_column(Integer, default=0)  # 大屏展示排序(越大越前)
+    status: Mapped[str] = mapped_column(String, default="draft")  # draft/pending/review/published/claimed/doing/completed/cancelled
+    claimed_by: Mapped[str | None] = mapped_column(ForeignKey("users.id"), nullable=True)
+    claimed_at: Mapped[str] = mapped_column(String, default="")
+    doing_at: Mapped[str] = mapped_column(String, default="")
     publisher_org_id: Mapped[str | None] = mapped_column(ForeignKey("organizations.id"), nullable=True)
     publisher_name: Mapped[str] = mapped_column(String, default="")
     created_at: Mapped[str] = mapped_column(String, default="")
     updated_at: Mapped[str] = mapped_column(String, default="")
 
 
+class TaskClaim(Base):
+    """任务接单流水（扫码/抢单/投标中标），rich 记录任务状态流转历史。"""
+
+    __tablename__ = "task_claims"
+
+    id: Mapped[str] = mapped_column(String, primary_key=True)
+    task_id: Mapped[str] = mapped_column(
+        ForeignKey("tasks.id", ondelete="CASCADE"), nullable=False, index=True,
+    )
+    claimer_user_id: Mapped[str] = mapped_column(
+        ForeignKey("users.id", ondelete="SET NULL"), nullable=True,
+    )
+    claimer_name: Mapped[str] = mapped_column(String, default="")
+    claim_source: Mapped[str] = mapped_column(String, default="scan")  # scan/grab/bid/dispatch
+    claimed_at: Mapped[str] = mapped_column(String, default="")
+    status: Mapped[str] = mapped_column(String, default="claimed")  # claimed/doing/completed/withdrawn
+    created_at: Mapped[str] = mapped_column(String, default="")
+    updated_at: Mapped[str] = mapped_column(String, default="")
+
+
 class ServiceProvider(Base):
     """服务商（运营端审核/评级/考核）。"""