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/models/update.rs

@@ -1,11 +1,9 @@
-use super::super::super::model::{
-    build_admin_provider_model_response, build_admin_provider_model_update_record,
-};
+use super::payloads::build_admin_provider_model_response;
+use super::write::build_admin_provider_model_update_record;
 use crate::control::GatewayControlDecision;
 use crate::control::GatewayPublicRequestContext;
-use crate::handlers::admin::provider::shared::{
-    admin_provider_model_route_parts, AdminProviderModelUpdateRequest,
-};
+use crate::handlers::admin::provider::shared::paths::admin_provider_model_route_parts;
+use crate::handlers::admin::provider::shared::payloads::AdminProviderModelUpdateRequest;
 use crate::{AppState, GatewayError};
 use axum::{
     body::{Body, Bytes},