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- Add LayoutMode enum (SINGLE_PANE/DECK) persisted in DesktopPreferences - SinglePaneLayout: NavigationRail + single content area reusing deck routing - View menu "Deck Layout" toggle with Cmd+Shift+D shortcut - Column resize: redistribute width on add/remove, double-click header to expand - Constrain drag resize to window bounds via BoxWithConstraints - FlowRow headers in FeedScreen/ReadsScreen to wrap on narrow columns Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>