feat: 个人用户聚合视图 — 客户管理双Tab+四模块数据聚合

- customers 表新增 customer_type 列 (unit/individual)
- 客户管理页：单位客户 | 个人用户 Tab 切换
- 个人用户 Tab: 直接内嵌4 Tab 显示所有个人用户的聚合数据
- 个人用户通过业务模块快速新建产生 (customer_type=individual)
- 4个业务API新增 customer_type 筛选参数（JOIN customers）
- 客户列表排序: 个人用户置顶

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

backend/app/main.py

@@ -42,6 +42,9 @@ async def lifespan(app: FastAPI):
         await conn.run_sync(lambda c: c.exec_driver_sql(
             "ALTER TABLE customers ADD COLUMN IF NOT EXISTS last_visit_manager_id UUID"
         ))
+        await conn.run_sync(lambda c: c.exec_driver_sql(
+            "ALTER TABLE customers ADD COLUMN IF NOT EXISTS customer_type VARCHAR(20) DEFAULT 'unit'"
+        ))
         # New columns for v0.4
         await conn.run_sync(lambda c: c.exec_driver_sql(
             "ALTER TABLE visits ADD COLUMN IF NOT EXISTS companion_names TEXT[] DEFAULT '{}'"