fix: 修复PR #458中的totalCostLimit功能问题

主要修复：
- 移除重复的totalUsageLimit字段，统一使用totalCostLimit
- 删除auth.js中重复的总费用限制检查逻辑
- 删除admin.js中重复的totalCostLimit验证代码
- 更新所有前端组件，移除totalUsageLimit引用

功能改进：
- 确保totalCostLimit作为永久累计费用限制正常工作
- 与dailyCostLimit（每日重置）功能互补
- 适用于预付费、一次性API Key场景

测试：
- 删除有逻辑错误的test-total-usage-limit.js
- 创建新的test-total-cost-limit.js验证功能正确性
- 所有测试通过，功能正常工作

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

web/admin-spa/src/components/apikeys/UsageDetailModal.vue

@@ -190,11 +190,11 @@
                 </span>
               </div>
 
-              <div v-if="apiKey.totalUsageLimit > 0" class="space-y-2">
+              <div v-if="apiKey.totalCostLimit > 0" class="space-y-2">
                 <div class="flex items-center justify-between text-sm">
                   <span class="text-gray-600 dark:text-gray-400">总费用限制</span>
                   <span class="font-semibold text-gray-900 dark:text-gray-100">
-                    ${{ apiKey.totalUsageLimit.toFixed(2) }}
+                    ${{ apiKey.totalCostLimit.toFixed(2) }}
                   </span>
                 </div>
                 <div class="h-2 w-full rounded-full bg-gray-200 dark:bg-gray-600">
@@ -275,7 +275,7 @@ const totalTokens = computed(() => props.apiKey.usage?.total?.tokens || 0)
 const dailyTokens = computed(() => props.apiKey.usage?.daily?.tokens || 0)
 const totalCost = computed(() => props.apiKey.usage?.total?.cost || 0)
 const dailyCost = computed(() => props.apiKey.dailyCost || 0)
-const totalUsageLimit = computed(() => props.apiKey.totalUsageLimit || 0)
+const totalCostLimit = computed(() => props.apiKey.totalCostLimit || 0)
 const inputTokens = computed(() => props.apiKey.usage?.total?.inputTokens || 0)
 const outputTokens = computed(() => props.apiKey.usage?.total?.outputTokens || 0)
 const cacheCreateTokens = computed(() => props.apiKey.usage?.total?.cacheCreateTokens || 0)
@@ -286,7 +286,7 @@ const tpm = computed(() => props.apiKey.usage?.averages?.tpm || 0)
 const hasLimits = computed(() => {
   return (
     props.apiKey.dailyCostLimit > 0 ||
-    props.apiKey.totalUsageLimit > 0 ||
+    props.apiKey.totalCostLimit > 0 ||
     props.apiKey.concurrencyLimit > 0 ||
     props.apiKey.rateLimitWindow > 0 ||
     props.apiKey.tokenLimit > 0
@@ -299,8 +299,8 @@ const dailyCostPercentage = computed(() => {
 })
 
 const totalUsagePercentage = computed(() => {
-  if (!totalUsageLimit.value || totalUsageLimit.value === 0) return 0
-  return (totalCost.value / totalUsageLimit.value) * 100
+  if (!totalCostLimit.value || totalCostLimit.value === 0) return 0
+  return (totalCost.value / totalCostLimit.value) * 100
 })
 
 // 方法