fix(frontend): 优化分组表单中订阅模式的字段显示逻辑

- 订阅模式下隐藏 Exclusive 字段并默认为开启状态
- 编辑分组时禁用计费类型字段，防止修改
- 移除编辑表单中无用的 subscription_type watch

frontend/src/i18n/locales/en.ts

@@ -543,6 +543,7 @@ export default {
         title: 'Subscription Settings',
         type: 'Billing Type',
         typeHint: 'Standard billing deducts from user balance. Subscription mode uses quota limits instead.',
+        typeNotEditable: 'Billing type cannot be changed after group creation.',
         standard: 'Standard (Balance)',
         subscription: 'Subscription (Quota)',
         dailyLimit: 'Daily Limit (USD)',

frontend/src/i18n/locales/zh.ts

@@ -598,6 +598,7 @@ export default {
         title: '订阅设置',
         type: '计费类型',
         typeHint: '标准计费从用户余额扣除。订阅模式使用配额限制。',
+        typeNotEditable: '分组创建后无法修改计费类型。',
         standard: '标准（余额）',
         subscription: '订阅（配额）',
         dailyLimit: '每日限额（USD）',

frontend/src/views/admin/GroupsView.vue

@@ -180,7 +180,7 @@
           />
           <p class="input-hint">{{ t('admin.groups.rateMultiplierHint') }}</p>
         </div>
-        <div class="flex items-center gap-3">
+        <div v-if="createForm.subscription_type !== 'subscription'" class="flex items-center gap-3">
           <button
             type="button"
             @click="createForm.is_exclusive = !createForm.is_exclusive"
@@ -323,7 +323,7 @@
             class="input"
           />
         </div>
-        <div class="flex items-center gap-3">
+        <div v-if="editForm.subscription_type !== 'subscription'" class="flex items-center gap-3">
           <button
             type="button"
             @click="editForm.is_exclusive = !editForm.is_exclusive"
@@ -360,8 +360,9 @@
             <Select
               v-model="editForm.subscription_type"
               :options="subscriptionTypeOptions"
+              :disabled="true"
             />
-            <p class="input-hint">{{ t('admin.groups.subscription.typeHint') }}</p>
+            <p class="input-hint">{{ t('admin.groups.subscription.typeNotEditable') }}</p>
           </div>
 
           <!-- Subscription limits (only show when subscription type is selected) -->
@@ -676,16 +677,11 @@ const confirmDelete = async () => {
   }
 }
 
-// 监听 subscription_type 变化，配额模式时重置 rate_multiplier 为 1
+// 监听 subscription_type 变化，订阅模式时重置 rate_multiplier 为 1，is_exclusive 为 true
 watch(() => createForm.subscription_type, (newVal) => {
   if (newVal === 'subscription') {
     createForm.rate_multiplier = 1.0
-  }
-})
-
-watch(() => editForm.subscription_type, (newVal) => {
-  if (newVal === 'subscription') {
-    editForm.rate_multiplier = 1.0
+    createForm.is_exclusive = true
   }
 })