feat: 波士顿产品矩阵 — 四象限分析(明星/现金牛/问题/瘦狗)

- 数据层: product_sales表+导入脚本(93条, 酣客1-8月商品销售排行榜)
- 后端: GET /api/cma/products/matrix?entity_id&months
  横轴=销售趋势(线性回归), 纵轴=加权毛利率, 气泡=销售额
- 前端: ProductMatrix.vue ECharts散点图+象限卡片+明细表, 支持酣客/博海切换
- 验证: API四象限分类正确, 数据联动, 前端路由200, 全部通过

backend/app/models/__init__.py

@@ -6,6 +6,7 @@ from app.models.budget_plan import BudgetPlan
 from app.models.cost_model import StandardCost, ActualCost, AbcActivity, AbcAllocation
 from app.models.knowledge import KnowledgeEvent, KnowledgeSummary
 from app.models.driver_budget import DriverFactorTemplate, DriverFactorBudget
+from app.models.product_sales import ProductSales
 
 
 class Entity(Base):