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.

components/ui/Button.tsx

@@ -0,0 +1,43 @@
+import { ButtonHTMLAttributes, forwardRef } from 'react';
+import { cn } from '@/lib/utils';
+
+interface ButtonProps extends ButtonHTMLAttributes<HTMLButtonElement> {
+  variant?: 'primary' | 'secondary' | 'danger' | 'ghost';
+  size?: 'sm' | 'md' | 'lg';
+}
+
+const Button = forwardRef<HTMLButtonElement, ButtonProps>(
+  ({ className, variant = 'primary', size = 'md', ...props }, ref) => {
+    const baseStyles = 'inline-flex items-center justify-center font-mono font-medium transition-all duration-200 focus:outline-none focus:ring-2 focus:ring-offset-2 focus:ring-offset-slate-950 disabled:opacity-50 disabled:cursor-not-allowed';
+    
+    const variants = {
+      primary: 'bg-cyan-600 hover:bg-cyan-500 text-white border border-cyan-500/30 shadow-cyan-500/20 shadow-lg hover:shadow-cyan-500/30 focus:ring-cyan-500',
+      secondary: 'bg-slate-800 hover:bg-slate-700 text-slate-100 border border-slate-600 shadow-slate-500/20 shadow-lg hover:shadow-slate-500/30 focus:ring-slate-500',
+      danger: 'bg-red-600 hover:bg-red-500 text-white border border-red-500/30 shadow-red-500/20 shadow-lg hover:shadow-red-500/30 focus:ring-red-500',
+      ghost: 'bg-transparent hover:bg-slate-800/50 text-slate-300 hover:text-slate-100 border border-slate-700/50 hover:border-slate-600 focus:ring-slate-500'
+    };
+    
+    const sizes = {
+      sm: 'px-3 py-1.5 text-xs rounded-md',
+      md: 'px-4 py-2 text-sm rounded-lg',
+      lg: 'px-6 py-3 text-base rounded-lg'
+    };
+    
+    return (
+      <button
+        className={cn(
+          baseStyles,
+          variants[variant],
+          sizes[size],
+          className
+        )}
+        ref={ref}
+        {...props}
+      />
+    );
+  }
+);
+
+Button.displayName = 'Button';
+
+export { Button };