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.

assets/admin/src/router/component-loaders/shop.js

@@ -1,2 +0,0 @@
-// Shop ops Vue pages removed (Phase 4). Config uses SchemaPage.
-export const shopPageLoaders = {}

assets/admin/src/router/index.js

@@ -73,7 +73,7 @@ function createSectionRedirectRoutes() {
 
 /**
  * Old SPA ops routes → native WP admin pages (Phase 4 transition).
- * Bookmarks under #/shop/products etc. land on NativeOpsRedirect.
+ * Bookmarks under order-related paths land on NativeOpsRedirect.
  */
 const NATIVE_OPS_REDIRECTS = [
   { path: '/payment/charge-card', title: '充值卡', nativeAdminPath: 'admin.php?page=aksrt_charge_cards' },