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>

alembic/versions/f9f4eaef2e6f_task_claims_and_task_display_fields.py

@@ -0,0 +1,59 @@
+"""task claims and task display fields
+
+Revision ID: f9f4eaef2e6f
+Revises: 0007_user_classification
+Create Date: 2026-08-25 18:23:09.123825
+
+仅包含本次「任务中心 + 扫码接单」改动：tasks 增加展示/流转字段 + 新增 task_claims 流水表。
+（autogenerate 曾误带 training_* 删除与 users 列改动，已剔除，勿并入。）
+"""
+from __future__ import annotations
+
+import sqlalchemy as sa
+from alembic import op
+
+
+revision = 'f9f4eaef2e6f'
+down_revision = '0007_user_classification'
+branch_labels = None
+depends_on = None
+
+
+def upgrade() -> None:
+    # ---- task_claims 接单流水表 ----
+    op.create_table('task_claims',
+    sa.Column('id', sa.String(), nullable=False),
+    sa.Column('task_id', sa.String(), nullable=False),
+    sa.Column('claimer_user_id', sa.String(), nullable=True),
+    sa.Column('claimer_name', sa.String(), nullable=False, server_default=''),
+    sa.Column('claim_source', sa.String(), nullable=False, server_default='scan'),
+    sa.Column('claimed_at', sa.String(), nullable=False, server_default=''),
+    sa.Column('status', sa.String(), nullable=False, server_default='claimed'),
+    sa.Column('created_at', sa.String(), nullable=False, server_default=''),
+    sa.Column('updated_at', sa.String(), nullable=False, server_default=''),
+    sa.ForeignKeyConstraint(['claimer_user_id'], ['users.id'], ondelete='SET NULL'),
+    sa.ForeignKeyConstraint(['task_id'], ['tasks.id'], ondelete='CASCADE'),
+    sa.PrimaryKeyConstraint('id')
+    )
+    op.create_index(op.f('ix_task_claims_task_id'), 'task_claims', ['task_id'], unique=False)
+
+    # ---- tasks 增加展示/流转字段 ----
+    op.add_column('tasks', sa.Column('task_code', sa.String(), nullable=True))
+    op.add_column('tasks', sa.Column('tags', sa.String(), nullable=True))
+    op.add_column('tasks', sa.Column('display_priority', sa.Integer(), nullable=True))
+    op.add_column('tasks', sa.Column('claimed_by', sa.String(), nullable=True))
+    op.add_column('tasks', sa.Column('claimed_at', sa.String(), nullable=True))
+    op.add_column('tasks', sa.Column('doing_at', sa.String(), nullable=True))
+    op.create_index(op.f('ix_tasks_task_code'), 'tasks', ['task_code'], unique=False)
+
+
+def downgrade() -> None:
+    op.drop_index(op.f('ix_tasks_task_code'), table_name='tasks')
+    op.drop_column('tasks', 'doing_at')
+    op.drop_column('tasks', 'claimed_at')
+    op.drop_column('tasks', 'claimed_by')
+    op.drop_column('tasks', 'display_priority')
+    op.drop_column('tasks', 'tags')
+    op.drop_column('tasks', 'task_code')
+    op.drop_index(op.f('ix_task_claims_task_id'), table_name='task_claims')
+    op.drop_table('task_claims')