fix: Setup Token 账号使用真实 utilization 值替代状态估算

从响应头 anthropic-ratelimit-unified-5h-utilization 获取并存储真实
utilization 值，解决进度条始终显示 0% 的问题。窗口重置时清除旧值，
避免残留上个窗口的数据。

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

backend/internal/service/account_usage_service.go

@@ -2,6 +2,7 @@ package service
 
 import (
 	"context"
+	"encoding/json"
 	"fmt"
 	"log"
 	"strings"
@@ -666,15 +667,30 @@ func (s *AccountUsageService) estimateSetupTokenUsage(account *Account) *UsageIn
 			remaining = 0
 		}
 
-		// 根据状态估算使用率 (百分比形式，100 = 100%)
+		// 优先使用响应头中存储的真实 utilization 值（0-1 小数，转为 0-100 百分比）
 		var utilization float64
-		switch account.SessionWindowStatus {
-		case "rejected":
-			utilization = 100.0
-		case "allowed_warning":
-			utilization = 80.0
-		default:
-			utilization = 0.0
+		var found bool
+		if stored, ok := account.Extra["session_window_utilization"]; ok {
+			switch v := stored.(type) {
+			case float64:
+				utilization = v * 100
+				found = true
+			case json.Number:
+				if f, err := v.Float64(); err == nil {
+					utilization = f * 100
+					found = true
+				}
+			}
+		}
+
+		// 如果没有存储的 utilization，回退到状态估算
+		if !found {
+			switch account.SessionWindowStatus {
+			case "rejected":
+				utilization = 100.0
+			case "allowed_warning":
+				utilization = 80.0
+			}
 		}
 
 		info.FiveHour = &UsageProgress{