[Desktop parity] Dark theme is legacy dark mode instead of new dark theme

Observed behaviour

The dark theme is the legacy theme. (Image contains the desktop app using the legacy theme on the left, and the flutter app using the default dark theme on the right.)

Reproduction steps

Go to Settings -> Application -> Look & Feel -> Theme, and select the non-OLED dark theme.

Build information

Version 1.0.0, Beta 64, Channel Beta, Build 71, iOS 26.6 (arm64), Device iPad13,18, Locale en-US, Push apns, Flutter 3.47.4, Dart 3.13.3

Platform

iOS

Details

Expected behaviour Since desktop has both the "new" dark theme and the legacy option, but Flutter has only one of the two, I figure it'd correspond to the newer dark theme on desktop Canary.