List one page of account members at a time

Since administrators were grouped apart from members (b52c318), the account
settings page loads every user to split them and renders all of them. The
lazy next page still starts at the 501st user, so on an account with more
than 500 people, scrolling down lists those users a second time.

Load administrators on their own and page only members, both on the settings
page and on the pages that follow it.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_0142qgjggdJ2KDdGk7RF9Xm9

test/controllers/accounts_controller_test.rb

@@ -42,6 +42,18 @@ class AccountsControllerTest < ActionDispatch::IntegrationTest
     end
   end
 
+  test "edit lists a page of members and the next page carries on from it" do
+    User.insert_all 501.times.map { |i| { name: "Member #{i}", email_address: "member#{i}@37signals.com" } }
+
+    get edit_account_url
+    first_page = listed_user_ids
+    get account_users_url(page: 2, format: :turbo_stream)
+    next_page = listed_user_ids
+
+    assert_not_empty next_page
+    assert_equal User.active.without_bots.ids.sort, (first_page + next_page).sort
+  end
+
   test "update" do
     assert users(:david).administrator?
 
@@ -58,4 +70,9 @@ class AccountsControllerTest < ActionDispatch::IntegrationTest
     put account_url, params: { account: { name: "Different" } }
     assert_response :forbidden
   end
+
+  private
+    def listed_user_ids
+      response.body.scan(/id="role_user_(\d+)"/).flatten.map(&:to_i)
+    end
 end