Six tabs forced iPhone to spill Course into the system "More" tab, whose
own NavigationStack nested with CourseView's and produced a double back
chevron on every week/deck push. Drop the Settings tab, reach it from a
gear button on Dashboard that presents SettingsView as a sheet, and keep
the visible tab count at five so no More overflow exists.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
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