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/users.go

@@ -125,53 +125,63 @@ func handleGetUsers(c *gin.Context) {
 
 		appHeartbeatTimeoutMap = make(map[uint]int)
 
-		for _, app := range ownApps {
+		ownAppIDs := make([]uint, len(ownApps))
+		for i, app := range ownApps {
+			ownAppIDs[i] = app.ID
 			timeout := app.HeartbeatTimeout
 			if timeout == 0 {
 				timeout = 300
 			}
 			appHeartbeatTimeoutMap[app.ID] = timeout
+		}
 
-			var appUsers []model.AppUser
-			if err := database.DB.Preload("Application").Where("application_id = ?", app.ID).Find(&appUsers).Error; err != nil {
+		if len(ownAppIDs) > 0 {
+			if err := database.DB.Preload("Application").Where("application_id IN ?", ownAppIDs).Find(&users).Error; err != nil {
 				response.Error(c, 500, "获取用户列表失败")
 				return
 			}
-			users = append(users, appUsers...)
 		}
 
-		for _, agentApp := range agentApps {
-			var app model.Application
-			if err := database.DB.First(&app, agentApp.ApplicationID).Error; err != nil {
-				log.Printf("[DEBUG] Failed to get application %d: %v", agentApp.ApplicationID, err)
-				continue
-			}
+		agentAppIDs := make([]uint, len(agentApps))
+		for i, agentApp := range agentApps {
+			agentAppIDs[i] = agentApp.ApplicationID
+		}
 
-			log.Printf("[DEBUG] Processing agent app: ApplicationID=%d, AppName=%s", app.ID, app.Name)
+		var agentAppModels []model.Application
+		if len(agentAppIDs) > 0 {
+			database.DB.Where("id IN ?", agentAppIDs).Find(&agentAppModels)
+		}
 
+		agentAppMap := make(map[uint]model.Application)
+		for _, app := range agentAppModels {
+			agentAppMap[app.ID] = app
 			timeout := app.HeartbeatTimeout
 			if timeout == 0 {
 				timeout = 300
 			}
 			appHeartbeatTimeoutMap[app.ID] = timeout
+		}
 
-			var cardUserIDs []uint
-			if err := database.DB.Model(&model.Card{}).
-				Where("creator_id = ? AND application_id = ? AND app_user_id IS NOT NULL", userID, app.ID).
-				Pluck("app_user_id", &cardUserIDs).Error; err != nil {
-				log.Printf("[DEBUG] Failed to get card user IDs for app %d: %v", app.ID, err)
+		var allCardUserIDs []uint
+		for _, agentApp := range agentApps {
+			app, exists := agentAppMap[agentApp.ApplicationID]
+			if !exists {
 				continue
 			}
+			log.Printf("[DEBUG] Processing agent app: ApplicationID=%d, AppName=%s", app.ID, app.Name)
 
-			log.Printf("[DEBUG] Found %d card user IDs for app %d: %v", len(cardUserIDs), app.ID, cardUserIDs)
+			var cardUserIDs []uint
+			database.DB.Model(&model.Card{}).
+				Where("creator_id = ? AND application_id = ? AND app_user_id IS NOT NULL", userID, app.ID).
+				Pluck("app_user_id", &cardUserIDs)
+			allCardUserIDs = append(allCardUserIDs, cardUserIDs...)
+		}
 
-			if len(cardUserIDs) > 0 {
-				var appUsers []model.AppUser
-				if err := database.DB.Preload("Application").Where("id IN ?", cardUserIDs).Find(&appUsers).Error; err != nil {
-					log.Printf("[DEBUG] Failed to get users for app %d: %v", app.ID, err)
-					continue
-				}
-				log.Printf("[DEBUG] Found %d users for app %d", len(appUsers), app.ID)
+		if len(allCardUserIDs) > 0 {
+			var appUsers []model.AppUser
+			if err := database.DB.Preload("Application").Where("id IN ?", allCardUserIDs).Find(&appUsers).Error; err != nil {
+				log.Printf("[DEBUG] Failed to get users: %v", err)
+			} else {
 				users = append(users, appUsers...)
 			}
 		}