feat: apply density factor to card, column, and board spacing

src/components/board/KanbanColumn.tsx

@@ -84,7 +84,7 @@ export function KanbanColumn({ column, onCardClick }: KanbanColumnProps) {
         strategy={verticalListSortingStrategy}
       >
         <ScrollArea className="flex-1 overflow-y-auto">
-          <ul ref={setDroppableNodeRef} className="flex min-h-[40px] list-none flex-col gap-2 p-2">
+          <ul ref={setDroppableNodeRef} className="flex min-h-[40px] list-none flex-col" style={{ gap: `calc(0.5rem * var(--density-factor))`, padding: `calc(0.5rem * var(--density-factor))` }}>
             {column.cardIds.map((cardId) => {
               const card = board?.cards[cardId];
               if (!card) return null;