feat(business): 新增业务数据七表及 V5 迁移（业务/明细/状态留痕/发货/回款/评级配置）

- businesses 五项汇总冗余列服务层事务内维护；毛利润不落库（派生值，M3 台账固化）
- 行级 product_category 折算锚点（#14）；回款 settlement_status 预置为 M3 防重锚点
- 评级等级种子四条（迁移+init-dev 双写）；编号前缀常量 YW/SH/HK
- 双轨 SQL 同步（V4/V5 重导，schema_sync+test_models 164 例全绿）

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

backend/tests/unit/test_models.py

@@ -29,6 +29,13 @@ EXPECTED_TABLES = {
     "products",
     "customers",
     "ownership_change_logs",
+    "businesses",
+    "business_items",
+    "business_status_logs",
+    "shipments",
+    "shipment_items",
+    "receipts",
+    "customer_rating_grades",
 }
 
 # 单复数同形的集合名词：本身即复数语义，不受「以 s 结尾」检查约束