Mastodon 4.6 adds profile Collections and two-factor controls

### Mastodon 4.6 — Release highlights: Collections, server controls, profiles, and newsletters. The update introduces Collections for curated lists of profiles with notifications and a 25-profile cap to reduce abuse, new server-administration controls including an option to require two-factor authentication, a redesigned in-place profile editor with accessibility improvements and tab controls, an opt-in email subscription feature for anonymous readers (disabled by default), and a simplified landing page variant for institutional servers.