refactor: flatten src/AKSRT → src (drop theme-identifier dir)

Move all domain folders from src/AKSRT/{Domain} to src/{Domain}; remap
Composer PSR-4 "AKSRT\\": "src/"; update audit script + README + ADR
paths; remove dead tools/build-psr4-map.php (scanned deleted inc/classes).

src/Payment/GatewayInterface.php

@@ -0,0 +1,62 @@
+<?php
+/**
+ * @package AKSRT
+ */
+
+namespace AKSRT\Payment;
+
+defined('ABSPATH') || exit;
+
+/**
+ * 支付网关统一接口
+ */
+interface GatewayInterface {
+    /**
+     * 创建支付单
+     *
+     * @param array $order 订单数据
+     * @return array{success: bool, payment_url?: string, payment_data?: array, message?: string}
+     */
+    public function create_payment(array $order): array;
+
+    /**
+     * 验证回调
+     *
+     * @param \WP_REST_Request $request 回调请求
+     * @return array{success: bool, order_number?: string, amount?: float, transaction_id?: string, message?: string}
+     */
+    public function verify_callback(\WP_REST_Request $request): array;
+
+    /**
+     * 查询支付状态
+     *
+     * @param string $order_number 订单号
+     * @return array{success: bool, status?: string, transaction_id?: string, message?: string}
+     */
+    public function query_status(string $order_number): array;
+
+    /**
+     * 退款
+     *
+     * @param string $order_number 订单号
+     * @param float  $amount       退款金额
+     * @param string $request_id  幂等退款请求号
+     * @return array{success: bool, status?: string, refund_id?: string, request_id?: string, message?: string}
+     */
+    public function refund(string $order_number, float $amount, string $request_id = ''): array;
+
+    /**
+     * 获取网关显示名称
+     */
+    public function get_name(): string;
+
+    /**
+     * 获取网关标识
+     */
+    public function get_id(): string;
+
+    /**
+     * 网关是否已配置
+     */
+    public function is_configured(): bool;
+}