feat: 项目流水拆分为确收与回款+费用明细两Tab + 数据迁移

后端:
- 新增 expense_data TEXT 列(columns.py迁移)
- 新增 data_split 迁移:旧 budget_data cost/paid → expense_data(幂等)
- sum_budget cost/paid → sum_expense cost/paid(routes.py/helpers.py)
- TABLES 配置加入 expense_data

前端:
- 项目详情弹窗Tab:基本信息→确收与回款→费用明细→执行信息→任务管理→活动
- 确收与回款Tab:月份/确收/毛利/回款/备注
- 费用明细Tab:月份/费用类型/应付/已付/备注
- 项目表格三视图(月/季/总)cost/paid来源切换为expense_data
- 保存逻辑分两路: budget_data(rev/gross/payment)+expense_data(cost/paid)

backend/migrations/__init__.py

@@ -18,6 +18,7 @@ def run_migrations():
     from migrations.tables import migrate_create_tables
     from migrations.columns import migrate_add_columns
     from migrations.data_fixes import migrate_fix_task_status, migrate_rename_tenant, migrate_drop_product_fields, migrate_fix_service_fee_standard
+    from migrations.data_split import migrate_data_split
     from migrations.seed import migrate_seed_users, migrate_seed_demo_data
 
     migrate_create_tables()
@@ -26,5 +27,6 @@ def run_migrations():
     migrate_rename_tenant()
     migrate_drop_product_fields()
     migrate_fix_service_fee_standard()
+    migrate_data_split()
     migrate_seed_users()
     migrate_seed_demo_data()