feat: real-time user profile updates and propagate avatarColor to all Avatar callsites

Broadcast user_updated events over WebSocket when profile fields change,
updating members, DM participants, friends, and cached messages in real time.
Widen useVoiceParticipantMeta to return the full user object and add a
standalone avatarColor prop to Avatar so all ~16 callsites now resolve
the user's chosen gradient color instead of falling back to hash-based colors.

packages/web/src/components/layout/ActivityPanel.tsx

@@ -68,6 +68,7 @@ export function ActivityPanel() {
           status={isOffline ? 'offline' : friend.status}
           className={isOffline ? 'opacity-60' : undefined}
           userId={friend.homeUserId ?? friend.id}
+          avatarColor={friend.avatarColor}
         />
         <div className="flex-1 min-w-0">
           <Username