refactor：项目架构重构和命名规范化

- 统一文件命名为snake_case格式（kebab-case  snake_case）
- 重构zulip模块为zulip_core，明确Core层职责
- 重构user-mgmt模块为user_mgmt，统一命名规范
- 调整模块依赖关系，优化架构分层
- 删除过时的文件和目录结构
- 更新相关文档和配置文件

本次重构涉及大量文件重命名和模块重组，
旨在建立更清晰的项目架构和统一的命名规范。

src/app.module.ts

@@ -11,10 +11,10 @@ import { AuthModule } from './business/auth/auth.module';
 import { ZulipModule } from './business/zulip/zulip.module';
 import { RedisModule } from './core/redis/redis.module';
 import { AdminModule } from './business/admin/admin.module';
-import { UserMgmtModule } from './business/user-mgmt/user-mgmt.module';
+import { UserMgmtModule } from './business/user_mgmt/user_mgmt.module';
 import { SecurityCoreModule } from './core/security_core/security_core.module';
-import { MaintenanceMiddleware } from './core/security_core/middleware/maintenance.middleware';
-import { ContentTypeMiddleware } from './core/security_core/middleware/content_type.middleware';
+import { MaintenanceMiddleware } from './core/security_core/maintenance.middleware';
+import { ContentTypeMiddleware } from './core/security_core/content_type.middleware';
 
 /**
  * 检查数据库配置是否完整 by angjustinl 2025-12-17