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.

assets/admin/src/schema/sections/payment/vip.js

@@ -208,7 +208,7 @@ export const vipSchema = {
           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；仅未开通会员可兑）',
         },
-        { 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 }, help: '显示在积分兑换弹窗底部，可以为提醒事项、兑换协议等，支持HTML代码' },
       ],
     },
     {