feat(phase1): core/ 基础设施迁移，旧路径改垫片

- core/: database/redis_client/jwt/password/response/exceptions/security/logger/deps/middleware/app
- create_app 迁移到 core/app.py，中间件注册顺序与异常处理器原样保留
- extensions/ utils/ apps/ 旧文件全部改为 re-export 垫片，import 路径保持兼容
- 新增 core 单元测试（jwt/password/response/request 共 12 个）

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

core/__init__.py

@@ -0,0 +1,13 @@
+# +======================================================================
+# | DjangoAdmin 企业数字化开发平台 [ 赋能开发者，助力企业发展 ]
+# +----------------------------------------------------------------------
+# | Copyright (c) 2021-2026 一米阳光团队 版权所有
+# | 开源协议: Apache-2.0
+# +======================================================================
+
+"""核心基础设施包：数据库、Redis、JWT、密码、响应、中间件、依赖注入。"""
+
+from core import response as R
+from core import password
+from core.database import get_db_session, SessionLocal, commit_independently, Base
+from core.redis_client import get_redis