chore(admin): clarify download points purchase mode copy

Rename residual 积分扣费/按次扣费 labels to 积分购买模式 and note cashier unlock; keep download_credit key for storage.

assets/admin/src/pages/CmsCredits.vue

@@ -89,12 +89,12 @@
     </n-card>
 
     <n-card class="aksrt-section-card">
-      <div class="aksrt-section-header"><h3>下载消费</h3></div>
+      <div class="aksrt-section-header"><h3>下载消费（参考）</h3></div>
       <n-form :model="cfg" label-placement="left" label-width="200" class="aksrt-form">
-        <n-form-item :label="`默认资源价格（${cfg.currency_name || '积分'}）`">
+        <n-form-item :label="`默认积分价参考（${cfg.currency_name || '积分'}）`">
           <n-input-number v-model:value="cfg.download_default_cost" :min="0" :max="100000" />
           <template #feedback>
-            <span class="aksrt-hint-text">资源未单独设价时回退使用。设为 0 表示免费</span>
+            <span class="aksrt-hint-text">兼容字段。实际价格以文章「付费内容设置」的积分价/现金价为准；下载解锁走收银台订单，不按次扣费。</span>
           </template>
         </n-form-item>
       </n-form>