fix(vip): let 积分兑换说明 support HTML like the reference theme

The points-exchange desc was stripped at all three layers: no sanitize_type on the schema fields (save ran sanitize_textarea_field), the runtime re-ran the same strip, and the points modal escaped it with esc_html. The reference theme declares sanitize=false and concatenates the value raw into the modal.

- Schema (SPA + PHP): sanitize_type html, rows 2, help text noting HTML support

- PaymentRuntime: output via wp_kses_post

- VipServiceModal points modal: render via wp_kses_post instead of esc_html

Verification: new contract test covers schema/runtime/modal layers; node --test tests/**/*.test.cjs 641/641 pass; php -l clean on both PHP files.

src/Admin/Schema/SchemaPayment.php

@@ -243,7 +243,7 @@ class SchemaPayment {
 						['key' => 'points-exchange', 'title' => '积分兑换会员', 'fields' => [
 							['key' => 'pay_vip_points_exchange_s', 'label' => '启用积分兑换', 'type' => 'switch', 'default' => false],
 							['key' => 'payment_vip_points_packages', 'label' => '兑换套餐', 'type' => 'textarea', 'default' => "1|500|30|积分月卡\n1|5000|0|积分永久", 'dependsOn' => ['key' => 'pay_vip_points_exchange_s', 'value' => true], 'help' => '每行：等级|积分|天数|标题（天数 0=永久；普通用户可开通，已有会员可续费同等级或升级更高等级）'],
-							['key' => 'pay_vip_points_exchange_desc', 'label' => '兑换说明', 'type' => 'textarea', 'default' => '', 'dependsOn' => ['key' => 'pay_vip_points_exchange_s', 'value' => true]],
+							['key' => 'pay_vip_points_exchange_desc', 'label' => '兑换说明', 'type' => 'textarea', 'sanitize_type' => 'html', 'default' => '', 'rows' => 2, 'dependsOn' => ['key' => 'pay_vip_points_exchange_s', 'value' => true]],
 						]],
 						['key' => 'modal-copy', 'title' => '界面文案', 'fields' => [
 							['key' => 'pay_user_vip_desc', 'label' => '会员介绍', 'type' => 'input', 'default' => '开通VIP会员，享受会员专属折扣以及多项特权', 'dependsOn' => ['any' => [['key' => 'pay_user_vip_1_s', 'value' => true], ['key' => 'pay_user_vip_2_s', 'value' => true]]]],