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/endpoint/mod.rs

@@ -1,52 +1,13 @@
-use crate::control::GatewayPublicRequestContext;
-use crate::handlers::admin::provider::{endpoint_keys, endpoints_admin};
-use crate::{AppState, GatewayError};
-use axum::body::{Body, Bytes};
-use axum::http::Response;
-
 mod extractors;
 mod health;
 mod health_builders;
+mod routes;
 mod rpm;
 
 pub(crate) use self::health_builders::build_admin_endpoint_health_status_payload;
-
-pub(crate) async fn maybe_build_local_admin_endpoints_response(
-    state: &AppState,
-    request_context: &GatewayPublicRequestContext,
-    request_body: Option<&Bytes>,
-) -> Result<Option<Response<Body>>, GatewayError> {
-    if let Some(response) =
-        health::maybe_build_local_admin_endpoints_health_response(state, request_context).await?
-    {
-        return Ok(Some(response));
-    }
-
-    if let Some(response) =
-        rpm::maybe_build_local_admin_endpoints_rpm_response(state, request_context).await?
-    {
-        return Ok(Some(response));
-    }
-
-    if let Some(response) = endpoint_keys::maybe_build_local_admin_endpoints_keys_response(
-        state,
-        request_context,
-        request_body,
-    )
-    .await?
-    {
-        return Ok(Some(response));
-    }
-
-    if let Some(response) = endpoints_admin::maybe_build_local_admin_endpoints_routes_response(
-        state,
-        request_context,
-        request_body,
-    )
-    .await?
-    {
-        return Ok(Some(response));
-    }
-
-    Ok(None)
-}
+pub(super) use self::health_builders::build_admin_health_summary_payload;
+pub(super) use self::health_builders::build_admin_key_health_payload;
+pub(super) use self::health_builders::build_admin_key_rpm_payload;
+pub(super) use self::health_builders::recover_admin_key_health;
+pub(super) use self::health_builders::recover_all_admin_key_health;
+pub(super) use self::routes::maybe_build_local_admin_endpoints_response;