feat(usage): 新增输出速度统计与请求详情性能分析

- 把 upstream_is_stream 物化到 usage 与 billing facts，避免 Provider 聚合回连 public.usage
- 统一前端标准/流式 TPS 计算与显示，流式按首字后生成耗时计算
- 新增请求详情抽屉展示单请求输出速度与 Provider 聚合 TPS

frontend/src/views/admin/PerformanceAnalysis.vue

@@ -594,7 +594,7 @@
                   {{ formatProviderPerformanceMetric(provider.success_rate, '%') }}
                 </td>
                 <td class="px-3 py-2 text-right">
-                  {{ formatProviderPerformanceMetric(provider.avg_output_tps, '/s') }}
+                  {{ formatProviderPerformanceMetric(provider.avg_output_tps, ' tps') }}
                 </td>
                 <td class="px-3 py-2 text-right">
                   {{ formatProviderPerformanceMetric(provider.avg_first_byte_time_ms, 'ms') }}
@@ -1093,7 +1093,7 @@ const providerPerformanceSummaryCards = computed(() => {
   return [
     {
       title: '输出 TPS',
-      value: formatProviderPerformanceMetric(summary?.avg_output_tps, '/s'),
+      value: formatProviderPerformanceMetric(summary?.avg_output_tps, ' tps'),
       hint: `请求 ${formatMetricNumber(summary?.request_count)}`,
       icon: Zap,
       iconClass: 'text-amber-500',
@@ -1142,7 +1142,7 @@ const providerTpsChartOptions = computed(() => ({
   scales: {
     y: {
       ticks: {
-        callback: (value: string | number) => `${value}/s`,
+        callback: (value: string | number) => `${value} tps`,
       },
     },
   },