Disable lndhub admin UI when not configured

app/controllers/admin/lightning_controller.rb

@@ -1,4 +1,6 @@
 class Admin::LightningController < Admin::BaseController
+  before_action :check_feature_enabled
+
   def index
     @current_section = :lightning
 
@@ -9,4 +11,11 @@ class Admin::LightningController < Admin::BaseController
     @ln[:current_balance] = LndhubAccount.current.joins(:ledgers).sum("account_ledgers.amount")
     @ln[:users_with_sats] = @accounts.length
   end
+
+  def check_feature_enabled
+    if ENV["LNDHUB_ADMIN_UI"].empty?
+      flash[:alert] = "Lightning Admin UI not enabled"
+      redirect_to admin_root_path and return
+    end
+  end
 end