feat: remove shop feature (Phase 2)

Delete all shop domain classes, controllers, schema builders, templates,
JS/CSS, admin SPA pages, and shop-only payment classes (Shipping,
AfterSale, Discount). Remove shop-only DB table definitions (product_variant,
after_sale, order_shipping, card_key) from migrator and add their DROP
to uninstall.php. Clean up shared files:

- Remove aksrt_product CPT + taxonomies from Setup.php
- Remove shop rewrite rules/query vars/template redirect from SetupPart2.php
- Remove shop widget areas from SetupPart1.php
- Remove shop enqueues from ScriptsPart1b.php
- Remove sepakerator-aksrt-shop from SetupPart2.php
- Remove get_shop_settings facade (delete ForumShop.php, clean DomainGroups.php)
- Remove ORDER_PRODUCT_SHOP constant from DomainModel.php
- Remove Shop::class fallback branches from UserOrders.php, OrderCenterRest.php
- Remove shipping/after-sale branches from OrderRepositoryAdmin.php, PayMenus.php, PayOrders.php
- Remove shop product widgets from widgets-register.php
- Remove cart page from template-registry.php, routing.php, ScriptsPart2.php
- Remove cart UI from sidebar-nav.php, profile-orders.php, sidebar-orders.php
- Clean up order-center.js (remove rebuy/cartUrl/receipt/after-sale handlers)
- Remove aksrt_get_cart_page_url/product_page/product_edit from transactions.php
- Clean up aksrt_product_cat references in Coupon.php, PayCoupons.php

Shared payment/order/credits/content-pay stack fully retained.

inc/helpers/user-center-renderers/sidebar-nav.php

@@ -7,19 +7,12 @@
 
 defined('ABSPATH') || exit;
 
-$cart_url = function_exists('aksrt_get_cart_page_url') ? aksrt_get_cart_page_url() : '';
 $level_url = isset($dashboard_tabs['level'])
 	? aksrt_get_user_center_tab_url('level')
 	: '';
 $auth_url = isset($dashboard_tabs['auth']) ? aksrt_get_user_center_tab_url('auth') : '';
 
 $services = array_values(array_filter([
-	[
-		'label' => __('购物车', 'aksrt'),
-		'icon'  => 'shopping-cart',
-		'tone'  => 'cart',
-		'url'   => $cart_url,
-	],
 	[
 		'label' => __('我的等级', 'aksrt'),
 		'icon'  => 'chart-line',