ChatPage's compactChrome was still using readSidebarEnabled() alone, but
PageRoutes now honors the explicit layoutMode setting (full/compact). When a
user sets layout to 'full' without portal login, PageRoutes shows chrome but
ChatPage didn't apply workspace-chat-bg, hiding the dark-blue theme background.
Now ChatPage mirrors PageRoutes' logic: prioritize layoutMode, fallback to
readSidebarEnabled() if unset.