Replace the 80dp NavigationRail + single content area with a TweetDeck-style
multi-column deck. Default layout: Home Feed + Notifications + Messages.
New deck system:
- DeckColumnType sealed class with 12 column types
- DeckState with StateFlow-based column management
- Per-column navigation stack for in-column drill-down
- Draggable dividers for column resize (300-800dp)
- Column config persisted via Jackson JSON in DesktopPreferences
- 48dp thin sidebar with add-column and settings buttons
- AddColumnDialog for picking column types
Keyboard shortcuts:
- Cmd+T: Add column
- Cmd+W: Close focused column
- Cmd+1-9: Focus column by index
- Cmd+Shift+Left/Right: Move column left/right
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
nrobi144
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