fix: federation avatar colors, cross-instance DMs, and instance persistence

- Fix avatar gradient colors in 7 UI sites by using homeUserId fallback
- Merge remote DM channels in populateFromReady (no longer home-only)
- Remove isHome guards from 8 DM WS event handlers for cross-instance DMs
- Route DM typing events to correct instance origin
- Fix autoConnectAll deleting disconnected instances from localStorage
- Distinguish network errors from auth errors in instance reconnection
- Start WebSocket retry for network-unreachable instances (auto-recovery)
- Add reconnectInstance method and Reconnect button in UI

packages/web/src/components/chat/MentionPopover.tsx

@@ -71,7 +71,7 @@ export function MentionPopover({ query, selectedIndex, onSelect }: MentionPopove
                 name={displayName}
                 size={24}
                 status={member.user.status}
-                userId={member.user.id}
+                userId={member.user.homeUserId ?? member.user.id}
               />
               <span
                 className="text-[14px] font-medium truncate"