DEV: Add code comments around oauth user-api-key/new handling (#31774)

Followup to #31759

app/controllers/users/omniauth_callbacks_controller.rb

@@ -87,6 +87,9 @@ class Users::OmniauthCallbacksController < ApplicationController
     cookies["_bypass_cache"] = true
     cookies[:authentication_data] = { value: client_hash.to_json, path: Discourse.base_path("/") }
 
+    # If the user account doesn't already exist, and this signup is part of a user-api-key request, direct
+    # the user to the homepage first so that signup can be completed. They'll be redirected to the user-api-key
+    # route once signup is complete. Hopefully, this can be simplified once fullscreen login/signup is everywhere.
     if !current_user && @origin.start_with?("/user-api-key/new")
       redirect_to path("/")
     else

lib/auth/result.rb

@@ -124,7 +124,8 @@ class Auth::Result
       AssociatedGroup.where(id: associated_group_ids).update_all("last_used = CURRENT_TIMESTAMP")
     end
 
-    Group.user_trust_level_change!(user.id, user.trust_level) if user && !user.staged
+    # refreshes automatic group membership (despite the name, it doesn't change TLs)
+    Group.user_trust_level_change!(user.id, user.trust_level) if user
   end
 
   def can_edit_name