fix(mobile): unfolding the Duo shows the sidebar as the split expands

UIKit applies the split's preferred display mode while a collapsed split
expands, before the new width reaches JS. The collapsed split asked for
secondaryOnly whenever a detail was open, so unfolding first hid the
sidebar and then slid it in once JS saw the wider window.

A collapsed split now carries the display mode the expanded split will
use, so the sidebar arrives with the expansion.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
b3ac8cde0aJulius Marminge committed on 10/21/2026, 11:43:06 PMparent29bdddb

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