refactor: 移除 Python upstream 依赖，清理全部 legacy/Python 兼容层

- 移除 upstream_base_url 参数及 AETHER_GATEWAY_UPSTREAM 环境变量，gateway 不再需要指向 Python 宿主
- 删除所有 LEGACY_*/PYTHON_* 常量、路由组、header 定义及 sunset/phaseout 机制
- 将 legacy_gateway_bridge 重命名为 internal_gateway，executor 相关命名统一为 execution_runtime
- dev.sh 新增 Postgres/Redis 预检查，移除 upstream 相关启动参数和提示
- 新增 ai_public 路由处理器
- 全量适配 handler、test、state、control 等模块的命名和接口变更

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

@@ -1,8 +1,15 @@
-use super::*;
+use crate::gateway::handlers::{query_param_value, unix_secs_to_rfc3339};
+use crate::gateway::{GatewayError, GatewayPublicRequestContext};
+use axum::{
+    body::Body,
+    http,
+    response::{IntoResponse, Response},
+    Json,
+};
+use serde_json::json;
 use sqlx::Row;
 
-const ADMIN_PAYMENTS_RUST_BACKEND_DETAIL: &str =
-    "Admin payments routes require Rust maintenance backend";
+const ADMIN_PAYMENTS_DATA_UNAVAILABLE_DETAIL: &str = "Admin payments data unavailable";
 
 #[derive(Debug, Default, serde::Deserialize)]
 pub(super) struct AdminPaymentOrderCreditRequest {
@@ -18,10 +25,10 @@ pub(super) struct AdminPaymentOrderCreditRequest {
     pub(super) gateway_response: Option<serde_json::Value>,
 }
 
-pub(super) fn build_admin_payments_maintenance_response() -> Response<Body> {
+pub(super) fn build_admin_payments_data_unavailable_response() -> Response<Body> {
     (
         http::StatusCode::SERVICE_UNAVAILABLE,
-        Json(json!({ "detail": ADMIN_PAYMENTS_RUST_BACKEND_DETAIL })),
+        Json(json!({ "detail": ADMIN_PAYMENTS_DATA_UNAVAILABLE_DETAIL })),
     )
         .into_response()
 }