Use zap comment for description/memo

But use the hashed zap request event for the description hash.

app/controllers/lnurlpay_controller.rb

@@ -131,10 +131,13 @@ class LnurlpayController < ApplicationController
         return
       end
 
+      desc = "Zap for #{@user.address}"
+      desc = "#{desc}: \"#{event.content}\"" if event.content.present?
+
       invoice = LndhubManager::CreateUserInvoice.call(
         user: @user, payload: {
           amount: amount, # sats
-          description: event.to_json,
+          description: desc,
           description_hash: Digest::SHA256.hexdigest(event.to_json),
         }
       )