style: adjust KanbanBoard layout

- Changed the flex gap from `gap-6` to `gap-4` for a tighter layout.
- Updated the container class to `w-full` for better responsiveness.
- No functional changes, purely a visual enhancement.

components/kanban/Board.tsx

@@ -56,7 +56,7 @@ export function KanbanBoard({ tasks }: KanbanBoardProps) {
   ];
 
   return (
-    <div className="flex gap-6 overflow-x-auto pb-6">
+    <div className="w-full flex gap-4 overflow-x-auto pb-6">
       {columns.map((column) => (
         <KanbanColumn
           key={column.id}