Viewing a thread in mobile app starts the scroll controller at the first message, not the most recent

Motivation
The user has to scroll an enormous amount to get to the most recent message

This appears to be fixed by #4702 (merged 2026-08-12) — thread opens now wait for authoritative hydration before settling on the latest reply. Reproduced the symptom on the current App Store build; the fix is on main but not yet in a shipped mobile release.