fix(billing): 按账号控制 OpenAI 长上下文计费

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

@@ -168,6 +168,11 @@
           <div class="text-sm">
             <div class="flex items-center gap-1.5">
               <span class="font-medium text-green-600 dark:text-green-400">${{ row.actual_cost?.toFixed(6) || '0.000000' }}</span>
+              <span
+                v-if="row.long_context_billing_applied"
+                data-testid="long-context-billing-marker"
+                class="inline-flex items-center rounded px-1 py-px text-[10px] font-semibold leading-tight bg-amber-100 text-amber-700 ring-1 ring-inset ring-amber-200 dark:bg-amber-500/20 dark:text-amber-300 dark:ring-amber-500/30"
+              >x2</span>
               <!-- Cost Detail Tooltip -->
               <div
                 class="group relative"