refactor: 拆分 gateway 单体为独立 crate，新增 systemd 部署方案

将 gateway 内部的 model-fetch、provider-transport、scheduler-core、
usage-runtime、video-tasks-core 模块提取为独立 crate；重构 gateway
内部模块结构（state/router/cache/data/query 等）；移除大量遗留模块
文件；新增 systemd 二进制部署骨架及相关文档；更新前端 usage 相关
API 和组件。

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

@@ -1,5 +1,6 @@
-use crate::gateway::handlers::{query_param_value, unix_secs_to_rfc3339};
-use crate::gateway::{GatewayError, GatewayPublicRequestContext};
+use crate::control::GatewayPublicRequestContext;
+use crate::handlers::{query_param_value, unix_secs_to_rfc3339};
+use crate::GatewayError;
 use axum::{
     body::Body,
     http,
@@ -196,7 +197,7 @@ pub(super) fn admin_payment_effective_status(
 }
 
 pub(super) fn build_admin_payment_order_payload(
-    record: &crate::gateway::AdminWalletPaymentOrderRecord,
+    record: &crate::AdminWalletPaymentOrderRecord,
 ) -> serde_json::Value {
     json!({
         "id": record.id,
@@ -249,7 +250,7 @@ pub(super) fn build_admin_payment_callback_payload(
 }
 
 pub(super) fn build_admin_payment_callback_payload_from_record(
-    record: &crate::gateway::state::AdminPaymentCallbackRecord,
+    record: &crate::state::AdminPaymentCallbackRecord,
 ) -> serde_json::Value {
     json!({
         "id": record.id,