fix(admin): 修复退款金额精度问题

- 显示完整余额精度，避免四舍五入导致的退款失败
- 添加"全部"按钮，一键填入完整余额
- 移除最小金额限制，支持任意正数金额

frontend/src/components/admin/user/UserBalanceModal.vue

@@ -3,14 +3,17 @@
     <form v-if="user" id="balance-form" @submit.prevent="handleBalanceSubmit" class="space-y-5">
       <div class="flex items-center gap-3 rounded-xl bg-gray-50 p-4 dark:bg-dark-700">
         <div class="flex h-10 w-10 items-center justify-center rounded-full bg-primary-100"><span class="text-lg font-medium text-primary-700">{{ user.email.charAt(0).toUpperCase() }}</span></div>
-        <div class="flex-1"><p class="font-medium text-gray-900">{{ user.email }}</p><p class="text-sm text-gray-500">{{ t('admin.users.currentBalance') }}: ${{ user.balance.toFixed(2) }}</p></div>
+        <div class="flex-1"><p class="font-medium text-gray-900">{{ user.email }}</p><p class="text-sm text-gray-500">{{ t('admin.users.currentBalance') }}: ${{ formatBalance(user.balance) }}</p></div>
       </div>
       <div>
         <label class="input-label">{{ operation === 'add' ? t('admin.users.depositAmount') : t('admin.users.withdrawAmount') }}</label>
-        <div class="relative"><div class="absolute left-3 top-1/2 -translate-y-1/2 font-medium text-gray-500">$</div><input v-model.number="form.amount" type="number" step="0.01" min="0.01" required class="input pl-8" /></div>
+        <div class="relative flex gap-2">
+          <div class="relative flex-1"><div class="absolute left-3 top-1/2 -translate-y-1/2 font-medium text-gray-500">$</div><input v-model.number="form.amount" type="number" step="any" min="0" required class="input pl-8" /></div>
+          <button v-if="operation === 'subtract'" type="button" @click="fillAllBalance" class="btn btn-secondary whitespace-nowrap">{{ t('admin.users.withdrawAll') }}</button>
+        </div>
       </div>
       <div><label class="input-label">{{ t('admin.users.notes') }}</label><textarea v-model="form.notes" rows="3" class="input"></textarea></div>
-      <div v-if="form.amount > 0" class="rounded-xl border border-blue-200 bg-blue-50 p-4"><div class="flex items-center justify-between text-sm"><span>{{ t('admin.users.newBalance') }}:</span><span class="font-bold">${{ calculateNewBalance().toFixed(2) }}</span></div></div>
+      <div v-if="form.amount > 0" class="rounded-xl border border-blue-200 bg-blue-50 p-4"><div class="flex items-center justify-between text-sm"><span>{{ t('admin.users.newBalance') }}:</span><span class="font-bold">${{ formatBalance(calculateNewBalance()) }}</span></div></div>
     </form>
     <template #footer>
       <div class="flex justify-end gap-3">
@@ -35,11 +38,30 @@ const emit = defineEmits(['close', 'success']); const { t } = useI18n(); const a
 const submitting = ref(false); const form = reactive({ amount: 0, notes: '' })
 watch(() => props.show, (v) => { if(v) { form.amount = 0; form.notes = '' } })
 
+// 格式化余额：显示完整精度，去除尾部多余的0
+const formatBalance = (value: number) => {
+  if (value === 0) return '0.00'
+  // 最多保留8位小数，去除尾部的0
+  const formatted = value.toFixed(8).replace(/\.?0+$/, '')
+  // 确保至少有2位小数
+  const parts = formatted.split('.')
+  if (parts.length === 1) return formatted + '.00'
+  if (parts[1].length === 1) return formatted + '0'
+  return formatted
+}
+
+// 填入全部余额
+const fillAllBalance = () => {
+  if (props.user) {
+    form.amount = props.user.balance
+  }
+}
+
 const calculateNewBalance = () => {
   if (!props.user) return 0
   const result = props.operation === 'add' ? props.user.balance + form.amount : props.user.balance - form.amount
   // 避免浮点数精度问题导致的 -0.00 显示
-  return result === 0 || Object.is(result, -0) ? 0 : result
+  return Math.abs(result) < 1e-10 ? 0 : result
 }
 const handleBalanceSubmit = async () => {
   if (!props.user) return
@@ -47,10 +69,8 @@ const handleBalanceSubmit = async () => {
     appStore.showError(t('admin.users.amountRequired'))
     return
   }
-  // 使用小数点后两位精度比较，避免浮点数精度问题
-  const amount = Math.round(form.amount * 100) / 100
-  const balance = Math.round(props.user.balance * 100) / 100
-  if (props.operation === 'subtract' && amount > balance) {
+  // 退款时验证金额不超过实际余额
+  if (props.operation === 'subtract' && form.amount > props.user.balance) {
     appStore.showError(t('admin.users.insufficientBalance'))
     return
   }

frontend/src/i18n/locales/en.ts

@@ -724,6 +724,7 @@ export default {
       withdraw: 'Withdraw',
       depositAmount: 'Deposit Amount',
       withdrawAmount: 'Withdraw Amount',
+      withdrawAll: 'All',
       currentBalance: 'Current Balance',
       depositNotesPlaceholder:
         'e.g., New user registration bonus, promotional credit, compensation, etc.',

frontend/src/i18n/locales/zh.ts

@@ -780,6 +780,7 @@ export default {
       withdraw: '退款',
       depositAmount: '充值金额',
       withdrawAmount: '退款金额',
+      withdrawAll: '全部',
       depositNotesPlaceholder: '例如：新用户注册奖励、活动充值、补偿充值等',
       withdrawNotesPlaceholder: '例如：服务问题退款、错误充值退回、账户注销退款等',
       notesOptional: '备注为可选项，有助于未来查账',