refactor: Simplify root user notification and remove global email variable

- Remove global `RootUserEmail` variable
- Modify channel testing and user notification methods to use `GetRootUser()`
- Update user cache and notification service to use more consistent user base type
- Add new channel test notification type

controller/channel-test.go

@@ -238,9 +238,7 @@ var testAllChannelsLock sync.Mutex
 var testAllChannelsRunning bool = false
 
 func testAllChannels(notify bool) error {
-	if common.RootUserEmail == "" {
-		common.RootUserEmail = model.GetRootUserEmail()
-	}
+
 	testAllChannelsLock.Lock()
 	if testAllChannelsRunning {
 		testAllChannelsLock.Unlock()
@@ -295,10 +293,7 @@ func testAllChannels(notify bool) error {
 		testAllChannelsRunning = false
 		testAllChannelsLock.Unlock()
 		if notify {
-			err := common.SendEmail("通道测试完成", common.RootUserEmail, "通道测试完成，如果没有收到禁用通知，说明所有通道都正常")
-			if err != nil {
-				common.SysError(fmt.Sprintf("failed to send email: %s", err.Error()))
-			}
+			service.NotifyRootUser(dto.NotifyTypeChannelTest, "通道测试完成", "所有通道测试已完成")
 		}
 	})
 	return nil

controller/user.go

@@ -870,9 +870,6 @@ func EmailBind(c *gin.Context) {
 		})
 		return
 	}
-	if user.Role == common.RoleRootUser {
-		common.RootUserEmail = email
-	}
 	c.JSON(http.StatusOK, gin.H{
 		"success": true,
 		"message": "",