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/services/task_service.py

@@ -18,11 +18,49 @@ class TaskService:
         self.db = db
 
     async def grab(self, task_id: str, actor: dict) -> dict:
-        """抢单：仅 published + grab 模式可抢，抢后置 in_progress。"""
+        """抢单（兼容旧入口）：published + grab → claimed，记录接单流水。"""
+        return await self.claim_by_id(task_id, actor, source="grab")
+
+    async def claim(self, task_code: str, actor: dict, source: str = "scan") -> dict:
+        """扫码/按短码接单：解析 task_code 后领单。"""
+        task = await self.db.tasks.get_by_code(task_code)
+        if task is None:
+            raise HTTPException(status_code=404, detail="任务不存在")
+        return await self.claim_by_id(task["id"], actor, source=source)
+
+    async def claim_by_id(self, task_id: str, actor: dict, source: str) -> dict:
+        """published + grab 模式 → claimed（claimed_by/claimed_at + TaskClaim 流水）。"""
         task = await self.db.tasks.get(task_id)
-        if task is None or task["status"] != "published" or task["mode"] != "grab":
-            raise HTTPException(status_code=400, detail="任务不可抢单")
-        return await self.db.tasks.set_status(task_id, "in_progress")
+        if task is None:
+            raise HTTPException(status_code=404, detail="任务不存在")
+        if task["status"] != "published":
+            raise HTTPException(status_code=400, detail="任务不可接单")
+        if task["mode"] != "grab":
+            raise HTTPException(status_code=400, detail="任务不支持扫码接单")
+        updated = await self.db.tasks.claim(task_id, actor["id"])
+        await self.db.task_claims.create(
+            task_id, actor["id"],
+            actor.get("nickname") or actor.get("username", ""), source,
+        )
+        return updated
+
+    async def start_doing(self, task_id: str, actor: dict) -> dict:
+        """claimed → doing。"""
+        task = await self.db.tasks.get(task_id)
+        if task is None:
+            raise HTTPException(status_code=404, detail="任务不存在")
+        if task["status"] != "claimed":
+            raise HTTPException(status_code=400, detail="任务未接单，无法开始")
+        return await self.db.tasks.set_doing(task_id)
+
+    async def complete(self, task_id: str, actor: dict) -> dict:
+        """doing → completed。"""
+        task = await self.db.tasks.get(task_id)
+        if task is None:
+            raise HTTPException(status_code=404, detail="任务不存在")
+        if task["status"] != "doing":
+            raise HTTPException(status_code=400, detail="任务未在进行中，无法完成")
+        return await self.db.tasks.set_status(task_id, "completed")
 
     async def bid(self, task_id: str, actor: dict, quote: int, plan: str) -> dict:
         """投标：仅 published + bid 模式可投。"""