feat: add empty state card component and integrate AI suggestion functionality

- Introduced the EmptyStateCard component to display contextual guidance when columns are empty.
- Enhanced the KanbanBoard and BoardView components to utilize the new EmptyStateCard for improved user experience.
- Added AI suggestion functionality to the empty state configuration, allowing users to generate ideas directly from the backlog column.
- Updated constants to define empty state configurations for various column types.

apps/ui/src/components/views/board-view.tsx

@@ -1287,6 +1287,8 @@ export function BoardView() {
           selectedFeatureIds={selectedFeatureIds}
           onToggleFeatureSelection={toggleFeatureSelection}
           onToggleSelectionMode={toggleSelectionMode}
+          isDragging={activeFeature !== null}
+          onAiSuggest={() => setShowPlanDialog(true)}
         />
       </div>