perf: 修复 cards.go 和 users.go 中的 N+1 查询问题

cards.go:
- 合并循环中的 Count 查询为单次 GROUP BY 查询

users.go:
- 合并 ownApps 循环查询为单次 IN 查询
- 合并 agentApps 循环查询为批量查询
- 减少数据库查询次数从 O(n) 到 O(1)

backend/internal/router/admin/cards.go

@@ -124,10 +124,32 @@ func handleGetCardTypes(c *gin.Context) {
 		log.Printf("[DEBUG] CardType %d: ID=%d, Name=%s, ApplicationID=%v\n", i, ct.ID, ct.Name, ct.ApplicationID)
 	}
 
+	cardTypeIDs := make([]uint, len(cardTypes))
+	for i, ct := range cardTypes {
+		cardTypeIDs[i] = ct.ID
+	}
+
+	type CardCount struct {
+		CardTypeID uint
+		Count      int64
+	}
+	var cardCounts []CardCount
+	if len(cardTypeIDs) > 0 {
+		database.DB.Model(&model.Card{}).
+			Select("card_type_id, COUNT(*) as count").
+			Where("card_type_id IN ?", cardTypeIDs).
+			Group("card_type_id").
+			Find(&cardCounts)
+	}
+
+	countMap := make(map[uint]int64)
+	for _, cc := range cardCounts {
+		countMap[cc.CardTypeID] = cc.Count
+	}
+
 	var cardTypesWithCount []map[string]interface{}
 	for _, ct := range cardTypes {
-		var count int64
-		database.DB.Model(&model.Card{}).Where("card_type_id = ?", ct.ID).Count(&count)
+		count := countMap[ct.ID]
 		log.Printf("[DEBUG] CardType ID=%d, Name=%s, GeneratedCount=%d\n", ct.ID, ct.Name, count)
 
 		cardTypeMap := map[string]interface{}{