feat: Phase 2 Aether Drift — chat component token migration + scroll fix
Migrate all 8 chat rendering components from Discord tokens to Aether Drift
design system: Message, MarkdownRenderer, MentionBadge, MentionPopover,
FriendsPage, TypingIndicator, Embed, ImagePreview. Eliminates ~83 discord-*
class references and ~24 hardcoded hex values from components/chat/.
Fix critical scroll regression from Phase 1 grid migration by adding explicit
grid-rows-[minmax(0,1fr)] and min-h-0 to AppLayout's grid container, restoring
the height constraint chain to MessageList's overflow-y-auto.
Jannis Braun
662eb8abc5