New collapsible 'Relays' group in the sidebar (chat/file/message relay) that
expands to show its items and persists open state. Homepage gets a matching
Relays card group, and areas are now split by faded separator bars like the
sidebar. Relay pages are placeholder 'coming soon' stubs (/relays/{kind}).
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
