feat: add balance display, user columns, device mgmt and sessions for agent

- Backend: add balance to agent stats API
- Backend: return full user details (balance, expiry, online_status, device_count, application) in agent users API
- Backend: export admin device/session handlers, add agent routes for devices and sessions
- Backend: add card type permission check and balance deduction for agent user creation
- Backend: extract checkAgentUserPermission helper, add user edit API
- Frontend: add balance card to agent dashboard
- Frontend: add application, online_status, device_count, balance, expiry_at columns to agent user table
- Frontend: add agent devices page (reuse admin data-table component)
- Frontend: add agent sessions page (reuse admin data-table component)
- Frontend: add devices and sessions to agent navigation and routes
- Add i18n keys for agent devices, sessions, user columns, dashboard balance

backend/internal/router/agent/agent.go

@@ -10,6 +10,7 @@ import (
 	"time"
 	"verification-platform-backend/internal/database"
 	"verification-platform-backend/internal/model"
+	"verification-platform-backend/internal/router/admin"
 	"verification-platform-backend/internal/service"
 	"verification-platform-backend/pkg/response"
 	"verification-platform-backend/pkg/utils"
@@ -35,6 +36,14 @@ func SetupAgentRoutes(r *gin.RouterGroup) {
 	r.GET("/cards/export", handleExportCards)
 	r.GET("/cloud-variables", handleGetCloudVariables)
 	r.GET("/cloud-variables/:id/records", handleGetCloudVariableRecords)
+
+	r.GET("/devices", admin.HandleGetDevices)
+	r.PUT("/devices/:id/status", admin.HandleUpdateDeviceStatus)
+	r.DELETE("/devices/:id", admin.HandleUnbindDevice)
+	r.POST("/devices/:id/force-offline", admin.HandleForceOfflineDevice)
+
+	r.GET("/sessions", admin.HandleGetSessions)
+	r.DELETE("/sessions/:id", admin.HandleDeleteSession)
 }
 
 func handleGetStats(c *gin.Context) {
@@ -68,6 +77,9 @@ func handleGetStats(c *gin.Context) {
 	var todayRevenue float64
 	database.DB.Model(&model.Card{}).Where("(agent_id = ? OR (agent_id IS NULL AND creator_id = ?)) AND DATE(created_at) = ?", userID, userID, today).Select("COALESCE(SUM(price), 0)").Scan(&todayRevenue)
 
+	var agent model.User
+	database.DB.First(&agent, userID)
+
 	response.Success(c, gin.H{
 		"totalApps":     totalApps,
 		"totalCards":   totalCards,
@@ -75,6 +87,7 @@ func handleGetStats(c *gin.Context) {
 		"totalRevenue": totalRevenue,
 		"todayCards":   todayCards,
 		"todayRevenue": todayRevenue,
+		"balance":      agent.Balance,
 	})
 }
 
@@ -482,10 +495,50 @@ func handleGetUsers(c *gin.Context) {
 		limit = pageSizeInt
 	}
 
-	database.DB.Where("id IN ?", appUserIDs).Order("created_at DESC").Limit(limit).Offset(offset).Find(&users)
+	database.DB.Preload("Application").Where("id IN ?", appUserIDs).Order("created_at DESC").Limit(limit).Offset(offset).Find(&users)
+
+	result := make([]gin.H, 0, len(users))
+	for _, u := range users {
+		var deviceCount int64
+		database.DB.Model(&model.UserDevice{}).Where("user_id = ?", u.ID).Count(&deviceCount)
+
+		onlineStatus := "offline"
+		if u.Status == "banned" {
+			onlineStatus = "banned"
+		} else if u.LastHeartbeatAt != nil {
+			lastHeartbeat := *u.LastHeartbeatAt
+			if time.Since(lastHeartbeat) < 5*time.Minute {
+				onlineStatus = "online"
+			}
+		}
+
+		item := gin.H{
+			"id":               u.ID,
+			"username":         u.Username,
+			"email":            u.Email,
+			"status":           u.Status,
+			"balance":          u.Balance,
+			"expiry_at":        u.ExpiryAt,
+			"last_login_at":    u.LastLoginAt,
+			"last_heartbeat_at": u.LastHeartbeatAt,
+			"device_count":     deviceCount,
+			"online_status":    onlineStatus,
+			"application_id":   u.ApplicationID,
+			"is_trial_user":    u.IsTrialUser,
+			"created_at":       u.CreatedAt,
+		}
+		if u.Application.ID > 0 {
+			item["application"] = gin.H{
+				"id":           u.Application.ID,
+				"name":         u.Application.Name,
+				"billing_type": u.Application.BillingType,
+			}
+		}
+		result = append(result, item)
+	}
 
 	response.Success(c, gin.H{
-		"users":          users,
+		"users":          result,
 		"total":          total,
 		"active_count":   activeCount,
 		"disabled_count": disabledCount,