feat(task): 完善任务系统 —— 分类字典/字段/四种接单方式/独占限额/交付时限

- Task 加 published_at/delivery_days/headcount/exclusive/publisher_id/category_id；新增 TaskCategory 分类字典表(35 类)。
- mode 归一 grab/bid/assign/recommend(旧 designated→assign、dispatch→recommend)；TaskService 加 assign/recommend/select_recommend，claim 支持独占/限额、published+claimed 均可抢(多人)。
- TaskClaim 支持 source=assign/recommend、status=assigned/recommended/withdrawn + count_active_by_task；TaskCategoryRepository；Database 装配 task_categories。
- 端口：operator GET /admin/task-categories + POST tasks/{id}/assign|recommend|select；opc 同；park /api/tasks 返回 mode/deadline/delivery_days/headcount/exclusive/publisher_name。
- 迁移 0009(tasks 加列+task_categories)已应用+stamp；seed 35 分类字典 + task 新字段(含独占/推荐演示) + 补种已初始化库。
- 测试 test_task_system.py(独占/限额/指派/推荐/list_published/publish/category)+补齐 test_task_claim 语义, 15 passed。

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

tests/test_task_system.py

@@ -0,0 +1,116 @@
+# -*- coding: utf-8 -*-
+"""任务系统完善：独占/限额/指派/推荐/字段（自包含内存库）。"""
+from __future__ import annotations
+
+from contextlib import asynccontextmanager
+
+import pytest
+from fastapi import HTTPException
+from sqlalchemy.ext.asyncio import async_sessionmaker, create_async_engine
+
+from app.infrastructure.models import Base, TaskCategory  # noqa: F401
+from app.infrastructure.repositories import Database
+from app.services.task_service import TaskService
+
+
+@asynccontextmanager
+async def _db():
+    engine = create_async_engine("sqlite+aiosqlite:///:memory:")
+    async with engine.begin() as conn:
+        await conn.run_sync(Base.metadata.create_all)
+    Session = async_sessionmaker(engine, expire_on_commit=False)
+    async with Session() as session:
+        yield Database(session=session)
+    await engine.dispose()
+
+
+def _task(mode="grab", **kw):
+    base = dict(task_code="TK-X", title="任务", mode=mode, status="published",
+                category="技术开发", delivery_days=10, headcount=0, exclusive=False)
+    base.update(kw)
+    return base
+
+
+@pytest.mark.asyncio
+async def test_exclusive_claim_rejects_second():
+    """独占任务仅一人可接。"""
+    async with _db() as db:
+        t = await db.tasks.create(_task(exclusive=True, headcount=1))
+        a = {"id": "u1", "username": "opc01", "nickname": "阿健"}
+        await TaskService(db).claim(t["task_code"], a, source="scan")
+        with pytest.raises(HTTPException):
+            await TaskService(db).claim(t["task_code"], {"id": "u2"}, "scan")
+
+
+@pytest.mark.asyncio
+async def test_headcount_limit_rejects_overflow():
+    """限额任务达上限后拒绝再接。"""
+    async with _db() as db:
+        t = await db.tasks.create(_task(headcount=2))
+        await TaskService(db).claim(t["task_code"], {"id": "u1"}, "scan")
+        await TaskService(db).claim(t["task_code"], {"id": "u2"}, "scan")
+        with pytest.raises(HTTPException):
+            await TaskService(db).claim(t["task_code"], {"id": "u3"}, "scan")
+
+
+@pytest.mark.asyncio
+async def test_assign_marks_claimed():
+    """指派：assign 模式 → claimed(claimed_by=taker) + TaskClaim assigned。"""
+    async with _db() as db:
+        t = await db.tasks.create(_task(mode="assign"))
+        await TaskService(db).assign(t["id"], "u_taker", {"id": "u_pub"})
+        assert t is not None
+        after = await db.tasks.get(t["id"])
+        assert after["status"] == "claimed"
+        assert after["claimed_by"] == "u_taker"
+        claims = await db.task_claims.list_by_task(t["id"])
+        assert claims[0]["status"] == "assigned" and claims[0]["claim_source"] == "assign"
+
+
+@pytest.mark.asyncio
+async def test_assign_rejects_non_assign_mode():
+    async with _db() as db:
+        t = await db.tasks.create(_task(mode="grab"))
+        with pytest.raises(HTTPException):
+            await TaskService(db).assign(t["id"], "u_taker", {})
+
+
+@pytest.mark.asyncio
+async def test_recommend_then_select():
+    """推荐：→ 候选人 recommended → 选定 → claimed + assigned，其余 withdrawn。"""
+    async with _db() as db:
+        t = await db.tasks.create(_task(mode="recommend"))
+        actor = {"id": "u_pub", "username": "pub"}
+        recs = await TaskService(db).recommend(t["id"], ["u1", "u2"], actor)
+        assert len(recs) == 2
+        assert all(r["status"] == "recommended" for r in recs)
+        after = await TaskService(db).select_recommend(t["id"], "u1", actor)
+        assert after["status"] == "claimed" and after["claimed_by"] == "u1"
+        claims = await db.task_claims.list_by_task(t["id"])
+        by_user = {c["claimer_user_id"]: c["status"] for c in claims}
+        assert by_user == {"u1": "assigned", "u2": "withdrawn"}
+
+
+@pytest.mark.asyncio
+async def test_list_published_returns_new_fields():
+    """大屏取数：list_published 返回新字段。"""
+    async with _db() as db:
+        t = await db.tasks.create(_task(delivery_days=21, headcount=5, exclusive=False, category_id="tc_08"))
+        items = await db.tasks.list_published()
+        found = next(i for i in items if i["id"] == t["id"])
+        for k in ("delivery_days", "headcount", "exclusive", "published_at", "publisher_id", "category_id"):
+            assert k in found
+
+
+@pytest.mark.asyncio
+async def test_publish_sets_published_at():
+    async with _db() as db:
+        t = await db.tasks.create(_task(status="pending"))
+        after = await db.tasks.publish(t["id"])
+        assert after["status"] == "published" and after["published_at"]
+
+
+@pytest.mark.asyncio
+async def test_category_list_empty_ok():
+    async with _db() as db:
+        assert await db.task_categories.list() == []