feat(db): 引入 Alembic 取代裸 DDL 迁移

- alembic init + env.py 接 settings/models metadata（asyncpg->psycopg2 同步 URL）
- 补 3 个 CheckConstraint 到 models（原只在裸 DDL）
- 离线生成初始迁移（31 表+约束+95 索引，全 sa.* 通用类型）
- init_db 用 _run_alembic_migrations（自动基线+upgrade head）替换 create_tables+ensure_schema_updates（删 92 行裸 DDL）
- 删破坏性 migrate_db.py（drop_all）
- 既有 DB 首次启动自动 stamp 基线，无需手动

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

src/shared/models/database.py

@@ -1,5 +1,5 @@
 # models/database.py
-from sqlalchemy import Column, Integer, String, Text, DateTime, Date, JSON, LargeBinary, Boolean, Float, ForeignKey, UniqueConstraint, Numeric
+from sqlalchemy import Column, Integer, String, Text, DateTime, Date, JSON, LargeBinary, Boolean, Float, ForeignKey, UniqueConstraint, Numeric, CheckConstraint
 from sqlalchemy.ext.declarative import declarative_base
 from sqlalchemy.sql import func
 from sqlalchemy.orm import relationship
@@ -662,6 +662,7 @@ class Inventory(Base):
     __tablename__ = "inventory"
     __table_args__ = (
         UniqueConstraint("product_id", "warehouse_id", name="uq_inventory_product_warehouse"),
+        CheckConstraint("quantity >= 0 AND locked_quantity >= 0 AND locked_quantity <= quantity", name="ck_inventory_qty_nonnegative"),
     )
 
     id = Column(Integer, primary_key=True, index=True)
@@ -740,6 +741,9 @@ class PurchaseOrder(Base):
 class PurchaseOrderItem(Base):
     """采购订单明细表"""
     __tablename__ = "purchase_order_items"
+    __table_args__ = (
+        CheckConstraint("quantity > 0 AND received_quantity >= 0 AND received_quantity <= quantity", name="ck_purchase_order_items_qty"),
+    )
     
     id = Column(Integer, primary_key=True, index=True)
     order_id = Column(Integer, ForeignKey("purchase_orders.id"), nullable=False)
@@ -860,6 +864,9 @@ class AnalysisMetrics(Base):
 class SalesOrderItem(Base):
     """销售订单明细表"""
     __tablename__ = "sales_order_items"
+    __table_args__ = (
+        CheckConstraint("quantity > 0 AND delivered_quantity >= 0 AND delivered_quantity <= quantity", name="ck_sales_order_items_qty"),
+    )
     
     id = Column(Integer, primary_key=True, index=True)
     order_id = Column(Integer, ForeignKey("sales_orders.id"), nullable=False)