Only support primary domain for Lightning Address

Part of the process of removing support for serving multiple domains
from a single akkounts instance.

Also puts the Lightning Address discovery routes under the .well-known
path. Combined, these changes simplify reverse-proxying to the
.well-known endpoints.

app/controllers/lnurlpay_controller.rb

@@ -1,6 +1,6 @@
 class LnurlpayController < ApplicationController
-  before_action :check_feature_enabled
-  before_action :find_user_by_address
+  before_action :check_service_available
+  before_action :find_user
 
   MIN_SATS = 10
   MAX_SATS = 1_000_000
@@ -9,7 +9,7 @@ class LnurlpayController < ApplicationController
   def index
     render json: {
       status: "OK",
-      callback: "https://accounts.kosmos.org/lnurlpay/#{@user.address}/invoice",
+      callback: "https://#{Setting.accounts_domain}/lnurlpay/#{@user.cn}/invoice",
       tag: "payRequest",
       maxSendable: MAX_SATS * 1000, # msat
       minSendable: MIN_SATS * 1000, # msat
@@ -69,9 +69,8 @@ class LnurlpayController < ApplicationController
 
   private
 
-  def find_user_by_address
-    address = params[:address].split("@")
-    @user = User.where(cn: address.first, ou: address.last).first
+  def find_user
+    @user = User.where(cn: params[:username], ou: Setting.primary_domain).first
     http_status :not_found if @user.nil?
   end
 
@@ -89,7 +88,7 @@ class LnurlpayController < ApplicationController
 
   private
 
-  def check_feature_enabled
+  def check_service_available
     http_status :not_found unless Setting.lndhub_enabled?
   end
 end