refactor(server): 清理无用导入与类型转换

- 移除测试/控制器中未使用的导入与实例
- bills/classroom-rentals 改用 ESM 导入替代 require
- bills.service 去掉多余断言、backfill 显式转字符串、main.ts void bootstrap

apps/server/src/database/database-migrations.backfill.ts

@@ -53,7 +53,7 @@ export async function backfillOrganizations(
                VALUES (?, ?, ?, ?, ?, ?, ?, ?, ?, CURRENT_TIMESTAMP, CURRENT_TIMESTAMP)`,
             [
               uuidV7(),
-              `ORG_${legacy.id}`,
+              `ORG_${String(legacy.id)}`,
               name,
               0,
               legacy.contact || null,