Merge upstream/css-cleanup into master

Resolves conflicts between upstream/master and upstream/css-cleanup:
- CSS: take css-cleanup versions (button/link style unification, comment cleanup,
  table .button styles, [name=cancel]/.auxiliary styles)
- application_helper.rb: use SVG icon for flash message close button (css-cleanup)
- users_test.rb: use single-quote style (css-cleanup), keep sole-admin test (master)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

config/routes.rb

@@ -27,8 +27,9 @@ Rails.application.routes.draw do
   # https://github.com/heartcombo/devise/issues/5786
   connection = ActiveRecord::Base.connection
   if connection.schema_version && connection.table_exists?(:users)
+    # NOTE: change helper prefix from *_registration to *_profile once possible
     devise_for :users, path: '', path_names: {registration: 'profile'},
-      controllers: {registrations: :registrations}
+      controllers: {registrations: 'user/profiles'}
   end
 
   resources :users, only: [:index, :show, :update] do
@@ -37,9 +38,7 @@ Rails.application.routes.draw do
   end
 
   unauthenticated do
-    as :user do
-      root to: redirect('/sign_in')
-    end
+    root to: redirect('/sign_in')
   end
   root to: redirect('/units'), as: :user_root