feat: 客户管理新增个人用户类型，双Tab分离管理

- customers 表新增 customer_type 列 (unit/individual)
- 列表按个人优先排序，支持 customer_type 筛选
- PC端 el-radio-group 切换：单位客户 | 个人用户
- 个人用户表单: 仅姓名+备注，隐藏行业/地址/业务/月费/客户经理/联系人
- 所有业务模块客户搜索下拉中个人用户置顶

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

backend/app/main.py

@@ -42,6 +42,10 @@ 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"
         ))
+        # v0.9 — customer_type for unit vs individual
+        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 '{}'"