Refactor RegisterPage into a two-step flow: credentials first, then
personalization (display name, avatar upload, avatar color). Replace the
dual-panel sliding layout with conditional rendering and CSS keyframe
animations to eliminate overflow-hidden clipping of focus rings.
Supporting changes:
- Server accepts avatarColor on registration
- Auth store resets all user-scoped stores on login/register/logout
- Voice store gains resetSession() for full session cleanup
- Sync presence status to federated instances
- Propagate presence_update to socialStore regardless of origin