fix(billing): 修复 OpenAI fast 档位计费并补齐展示

- 打通 service_tier 在 OpenAI HTTP、WS、passthrough 与 usage 记录中的传递
- 修正 priority/flex 计费逻辑，并将 fast 归一化为 priority
- 在用户端和管理端补齐服务档位与计费明细展示
- 补齐前后端测试，并修复 WS 限流信号重复持久化导致的全量回归失败

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

frontend/src/components/admin/usage/UsageTable.vue

@@ -228,6 +228,14 @@
               <span class="text-gray-400">{{ t('admin.usage.outputCost') }}</span>
               <span class="font-medium text-white">${{ tooltipData.output_cost.toFixed(6) }}</span>
             </div>
+            <div v-if="tooltipData && tooltipData.input_tokens > 0" class="flex items-center justify-between gap-4">
+              <span class="text-gray-400">{{ t('usage.inputTokenPrice') }}</span>
+              <span class="font-medium text-sky-300">{{ formatTokenPricePerMillion(tooltipData.input_cost, tooltipData.input_tokens) }} {{ t('usage.perMillionTokens') }}</span>
+            </div>
+            <div v-if="tooltipData && tooltipData.output_tokens > 0" class="flex items-center justify-between gap-4">
+              <span class="text-gray-400">{{ t('usage.outputTokenPrice') }}</span>
+              <span class="font-medium text-violet-300">{{ formatTokenPricePerMillion(tooltipData.output_cost, tooltipData.output_tokens) }} {{ t('usage.perMillionTokens') }}</span>
+            </div>
             <div v-if="tooltipData && tooltipData.cache_creation_cost > 0" class="flex items-center justify-between gap-4">
               <span class="text-gray-400">{{ t('admin.usage.cacheCreationCost') }}</span>
               <span class="font-medium text-white">${{ tooltipData.cache_creation_cost.toFixed(6) }}</span>
@@ -238,6 +246,10 @@
             </div>
           </div>
           <!-- Rate and Summary -->
+          <div class="flex items-center justify-between gap-6">
+            <span class="text-gray-400">{{ t('usage.serviceTier') }}</span>
+            <span class="font-semibold text-cyan-300">{{ getUsageServiceTierLabel(tooltipData?.service_tier, t) }}</span>
+          </div>
           <div class="flex items-center justify-between gap-6">
             <span class="text-gray-400">{{ t('usage.rate') }}</span>
             <span class="font-semibold text-blue-400">{{ (tooltipData?.rate_multiplier || 1).toFixed(2) }}x</span>
@@ -271,6 +283,8 @@
 import { ref } from 'vue'
 import { useI18n } from 'vue-i18n'
 import { formatDateTime, formatReasoningEffort } from '@/utils/format'
+import { formatTokenPricePerMillion } from '@/utils/usagePricing'
+import { getUsageServiceTierLabel } from '@/utils/usageServiceTier'
 import { resolveUsageRequestType } from '@/utils/usageRequestType'
 import DataTable from '@/components/common/DataTable.vue'
 import EmptyState from '@/components/common/EmptyState.vue'