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>

app/controllers/user/profiles_controller.rb

@@ -0,0 +1,37 @@
+class User::ProfilesController < Devise::RegistrationsController
+  def destroy
+    if current_user.sole_admin?
+      redirect_back fallback_location: edit_user_registration_path,
+        alert: t(".sole_admin")
+      return
+    end
+    super
+  end
+
+  protected
+
+  def build_resource(hash = {})
+    super
+    # Skip the email confirmation step when the admin has enabled this option
+    # via the web setup wizard (stored as the "skip_email_confirmation" Setting).
+    # The account becomes active immediately so the user can sign in right after
+    # registering.
+    resource.skip_confirmation! if Setting.get("skip_email_confirmation") == "true"
+  end
+
+  def update_resource(resource, params)
+    # Based on update_with_password()
+    if params[:password].blank?
+      params.delete(:password)
+      params.delete(:password_confirmation) if params[:password_confirmation].blank?
+    end
+
+    result = resource.update(params)
+    resource.clean_up_passwords
+    result
+  end
+
+  def after_inactive_sign_up_path_for(resource)
+    new_user_session_path
+  end
+end