v0.2.0: CRM/ERP 系统升级 - 清理 .gitignore 并移除误提交的 venv/env/db 文件

- 更新 .gitignore：全面覆盖环境变量、数据库、日志、缓存、上传文件
- 移除误跟踪的 server/venv/、crm_data.db、.env 文件
- 新增 server/.env.example 模板
- 新增合同管理、利润核算、AI教练等功能模块
- 新增 Playwright e2e 测试套件
- 前后端多项功能升级和 bug 修复

server/app/models/cost.py

@@ -0,0 +1,41 @@
+"""
+成本域 ORM 模型
+映射: erp_order_item_costs
+"""
+
+from __future__ import annotations
+
+import uuid
+from datetime import datetime
+
+from sqlalchemy import DateTime, ForeignKey, Numeric, func
+from sqlalchemy.dialects.postgresql import UUID
+from sqlalchemy.orm import Mapped, mapped_column, relationship
+
+from app.models.base import Base
+
+
+class ErpOrderItemCost(Base):
+    """订单明细成本快照表 —— 发货/确认瞬间锚定 MWA 成本"""
+    __tablename__ = "erp_order_item_costs"
+
+    id: Mapped[uuid.UUID] = mapped_column(
+        UUID(as_uuid=True), primary_key=True, default=uuid.uuid4
+    )
+    order_item_id: Mapped[uuid.UUID] = mapped_column(
+        UUID(as_uuid=True), ForeignKey("erp_order_items.id"), nullable=False, unique=True,
+        comment="关联订单明细"
+    )
+    purchase_unit_price: Mapped[float] = mapped_column(
+        Numeric(12, 4), nullable=False, comment="MWA 成本快照"
+    )
+    profit_amount: Mapped[float] = mapped_column(
+        Numeric(14, 2), default=0, comment="利润额 = (售价-成本)*数量"
+    )
+    profit_rate: Mapped[float] = mapped_column(
+        Numeric(5, 4), default=0, comment="利润率"
+    )
+    created_at: Mapped[datetime] = mapped_column(DateTime, server_default=func.now())
+
+    # 关系
+    order_item: Mapped["ErpOrderItem"] = relationship("ErpOrderItem", lazy="selectin")  # noqa: F821