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/provider/oauth/quota/shared.rs

@@ -1,4 +1,4 @@
-use crate::handlers::admin::provider::shared::{
+use crate::handlers::admin::provider::shared::payloads::{
     OAUTH_ACCOUNT_BLOCK_PREFIX, OAUTH_REFRESH_FAILED_PREFIX,
 };
 use crate::{AppState, GatewayError};