refactor: 拆分 admin handler 大文件为模块目录，消除 shared.rs 反模式

- endpoint_keys/pool/architecture 等大文件拆分为独立模块目录
- 删除 crud/query/strategy/system 中的 shared.rs，内容归位到各自模块
- endpoints_admin/models/oauth/write 等模块拆出 payloads/responses/support 子文件
- system/core 下多个 *_routes.rs 合并到 system_routes.rs
- 更新 refactor-execution-plan 文档进度

apps/aether-gateway/src/handlers/admin/system/shared/mod.rs

@@ -1,14 +1,5 @@
-mod configs;
-mod email_templates;
-mod modules;
-mod paths;
-mod settings;
-
-pub(crate) use self::configs::*;
-pub(crate) use self::email_templates::{
-    apply_admin_email_template_update, build_admin_email_template_payload,
-    build_admin_email_templates_payload, preview_admin_email_template, reset_admin_email_template,
-};
-pub(crate) use self::modules::*;
-pub(crate) use self::paths::*;
-pub(crate) use self::settings::*;
+pub(crate) mod configs;
+pub(crate) mod email_templates;
+pub(crate) mod modules;
+pub(crate) mod paths;
+pub(crate) mod settings;