refactor: 大规模模块拆分与重组，新增 aether-admin crate

- 新建独立 aether-admin crate 承载 admin 相关共享契约与纯辅助函数
- 拆分 ai_pipeline 下 kiro/private_envelope/conversion/planner 等大文件为子模块目录
- 重组 admin handlers 各业务域（billing/oauth/provider/system/users 等）为目录结构，移除 shared.rs/builders.rs 等反模式
- 移除 ai_pipeline runtime adapters 旧实现（claude/openai/gemini/kiro/vertex/antigravity 等），改由 provider transport 统一承载
- 移除 control_facade/execution_facade/auth_snapshot_facade 等冗余 facade 层
- 拆分 query/billing 与 query/monitoring 模块、state/runtime/payments 与 security 模块
- 扩展架构测试覆盖 admin_billing/admin_model/admin_users 等新模块
- 删除 docs/architecture/refactor-execution-plan.md 已完成的执行计划文档

apps/aether-gateway/src/handlers/admin/billing/payments/shared.rs

@@ -1,4 +1,4 @@
-use crate::control::GatewayPublicRequestContext;
+use crate::handlers::admin::request::AdminRequestContext;
 use crate::handlers::admin::shared::{query_param_value, unix_secs_to_rfc3339};
 use crate::{GatewayAdminPaymentCallbackView, GatewayError};
 use axum::{
@@ -175,11 +175,10 @@ pub(super) fn normalize_admin_payment_positive_number(
 }
 
 pub(super) fn admin_payment_operator_id(
-    request_context: &GatewayPublicRequestContext,
+    request_context: &AdminRequestContext<'_>,
 ) -> Option<String> {
     request_context
-        .control_decision
-        .as_ref()
+        .decision()
         .and_then(|decision| decision.admin_principal.as_ref())
         .map(|principal| principal.user_id.clone())
 }