feat(credits): exchange balance for points

Replace the legacy points-to-balance and external points purchase flows
with direct integer balance-to-points exchange. Enforce exchange and
points-transfer limits and capability checks across the UI and REST API.

assets/admin/src/schema/sections/users/credits.js

@@ -5,8 +5,6 @@ export const creditsSchema = {
   description: '积分规则、积分日志、用户积分管理。',
   defaults: {
     points_s: true,
-    points_pay_s: false,
-    points_rate: 100,
     points_name: '积分',
     points_decimal: 2,
     points_earn_daily_limit: 50,
@@ -43,12 +41,6 @@ export const creditsSchema = {
       icon: 'fas fa-coins',
       fields: [
         { key: 'points_s', label: '启用积分系统', type: 'switch', default: true },
-        { key: 'points_pay_s', label: '启用购买积分', type: 'switch', default: false, help: '对齐 zibll points_pay_s：允许用户用现金/余额购买积分。' },
-        { key: 'points_rate', label: '积分汇率（1元=N积分）', type: 'number', default: 100, min: 1, max: 10000, dependsOn: { key: 'points_pay_s', value: true } },
-        { key: 'pay_points_desc', label: '购买积分说明', type: 'textarea', default: '', dependsOn: { key: 'points_pay_s', value: true } },
-        { key: 'pay_points_product', label: '积分套餐', type: 'textarea', default: '', help: '每行：支付金额|积分数量|标题。留空则仅自定义数量。', dependsOn: { key: 'points_pay_s', value: true } },
-        { key: 'pay_points_product_custom_s', label: '允许自定义积分数量', type: 'switch', default: true, dependsOn: { key: 'points_pay_s', value: true } },
-        { key: 'pay_points_product_custom_limit', label: '自定义积分上限', type: 'number', default: 99999, min: 1, max: 999999, dependsOn: { key: 'points_pay_s', value: true } },
         { key: 'points_name', label: '积分名称', type: 'input', default: '积分' },
         { key: 'points_decimal', label: '积分小数位数', type: 'number', default: 2, min: 0, max: 4 },
       ],