fix(dashboard): prefer username in user usage trend

backend/internal/pkg/usagestats/usage_log_types.go

@@ -96,6 +96,7 @@ type UserUsageTrendPoint struct {
 	Date       string  `json:"date"`
 	UserID     int64   `json:"user_id"`
 	Email      string  `json:"email"`
+	Username   string  `json:"username"`
 	Requests   int64   `json:"requests"`
 	Tokens     int64   `json:"tokens"`
 	Cost       float64 `json:"cost"`        // 标准计费

backend/internal/repository/usage_log_repo.go

@@ -1114,6 +1114,7 @@ func (r *usageLogRepository) GetUserUsageTrend(ctx context.Context, startTime, e
 			TO_CHAR(u.created_at, '%s') as date,
 			u.user_id,
 			COALESCE(us.email, '') as email,
+			COALESCE(us.username, '') as username,
 			COUNT(*) as requests,
 			COALESCE(SUM(u.input_tokens + u.output_tokens + u.cache_creation_tokens + u.cache_read_tokens), 0) as tokens,
 			COALESCE(SUM(u.total_cost), 0) as cost,
@@ -1122,7 +1123,7 @@ func (r *usageLogRepository) GetUserUsageTrend(ctx context.Context, startTime, e
 		LEFT JOIN users us ON u.user_id = us.id
 		WHERE u.user_id IN (SELECT user_id FROM top_users)
 		  AND u.created_at >= $4 AND u.created_at < $5
-		GROUP BY date, u.user_id, us.email
+		GROUP BY date, u.user_id, us.email, us.username
 		ORDER BY date ASC, tokens DESC
 	`, dateFormat)
 
@@ -1142,7 +1143,7 @@ func (r *usageLogRepository) GetUserUsageTrend(ctx context.Context, startTime, e
 	results = make([]UserUsageTrendPoint, 0)
 	for rows.Next() {
 		var row UserUsageTrendPoint
-		if err = rows.Scan(&row.Date, &row.UserID, &row.Email, &row.Requests, &row.Tokens, &row.Cost, &row.ActualCost); err != nil {
+		if err = rows.Scan(&row.Date, &row.UserID, &row.Email, &row.Username, &row.Requests, &row.Tokens, &row.Cost, &row.ActualCost); err != nil {
 			return nil, err
 		}
 		results = append(results, row)

frontend/src/types/index.ts

@@ -1155,6 +1155,7 @@ export interface UserUsageTrendPoint {
   date: string
   user_id: number
   email: string
+  username: string
   requests: number
   tokens: number
   cost: number // 标准计费

frontend/src/views/admin/DashboardView.vue

@@ -415,23 +415,29 @@ const lineOptions = computed(() => ({
 const userTrendChartData = computed(() => {
   if (!userTrend.value?.length) return null
 
-  // Extract display name from email (part before @)
-  const getDisplayName = (email: string, userId: number): string => {
-    if (email && email.includes('@')) {
-      return email.split('@')[0]
+  const getDisplayName = (point: UserUsageTrendPoint): string => {
+    const username = point.username?.trim()
+    if (username) {
+      return username
     }
-    return t('admin.redeem.userPrefix', { id: userId })
+
+    const email = point.email?.trim()
+    if (email) {
+      return email
+    }
+
+    return t('admin.redeem.userPrefix', { id: point.user_id })
   }
 
-  // Group by user
-  const userGroups = new Map<string, { name: string; data: Map<string, number> }>()
+  // Group by user_id to avoid merging different users with the same display name
+  const userGroups = new Map<number, { name: string; data: Map<string, number> }>()
   const allDates = new Set<string>()
 
   userTrend.value.forEach((point) => {
     allDates.add(point.date)
-    const key = getDisplayName(point.email, point.user_id)
+    const key = point.user_id
     if (!userGroups.has(key)) {
-      userGroups.set(key, { name: key, data: new Map() })
+      userGroups.set(key, { name: getDisplayName(point), data: new Map() })
     }
     userGroups.get(key)!.data.set(point.date, point.tokens)
   })