refactor(db): 数据库模块分层重构，抽取基础设施并迁移业务复现逻辑
- db_core: 新增通用数据库基础设施(Database/连接工厂/Nacos配置缓存)
- location_map/db/queries: 按业务域拆分查询层(tenant/brand/competitor/ branch_company/city/cluster/chance_point/standard/mirage/divebomb)
- location_map/db/oracles: 接口 expected/oracle 层(approval/brand/dashboard/ data_migration/mall/mirage/spot_evaluation/task/youth_map)
- common/database.py 缩为兼容门面，database_location/mirage/divebomb 缩为兼容模块
- 全部测试文件与公共方法 import 迁移到新路径
- tests/unit/test_database_architecture.py: 分层/无循环依赖/兼容导出架构测试
- workbuddy/skills: 更新 DB 校验编写规范