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/Content/VipServiceModal.php

@@ -238,7 +238,9 @@ trait VipServiceModal {
 
         $desc_text = trim((string) ($points_ex['desc'] ?? ''));
         $desc = $desc_text !== ''
-            ? '<div class="muted-box muted-2-color padding-10 em09 mt20">' . esc_html($desc_text) . '</div>'
+            // 管理员编辑的富文本说明：保存端已 wp_kses_post，这里同级别输出
+            // （参考主题 zibpay_get_vip_points_exchange_modal 原样拼接）。
+            ? '<div class="muted-box muted-2-color padding-10 em09 mt20">' . wp_kses_post($desc_text) . '</div>'
             : '';
 
         // 最低价套餐仍超出用户积分 → 参考主题的 badg c-red btn-block 提示。