add page exit for page_migrate

app/controllers/projects_controller.rb

@@ -100,6 +100,8 @@ class ProjectsController < ApplicationController
 
   def page_migrate
     return normal_status(-1, "您还未开通Page服务，无法进行新建站点") unless current_user.id_card_verify
+    return normal_status(-1, "你已使用了 #{page_site_params[:identifier]} 作为page标识") if Page.exists?(identifier: page_site_params[:identifier], user: current_user)
+    
     Projects::MigrateForm.new(mirror_params).validate!
 
     @project =