feat: add clsx and tailwind-merge dependencies, enhance Kanban components

- Added `clsx` and `tailwind-merge` to `package.json` and `package-lock.json` for improved class management and utility merging.
- Updated `Column` and `TaskCard` components to utilize new UI components (`Card`, `Badge`) for a more cohesive design.
- Refactored styles in `Header` and Kanban components to align with the new design system.
- Marked several tasks as completed in `TODO.md` reflecting progress on UI enhancements.

lib/utils.ts

@@ -0,0 +1,9 @@
+import { type ClassValue, clsx } from 'clsx';
+import { twMerge } from 'tailwind-merge';
+
+/**
+ * Utility function to merge Tailwind CSS classes
+ */
+export function cn(...inputs: ClassValue[]) {
+  return twMerge(clsx(inputs));
+}