feat: implement Figlet, Pastel, and Unit tools with a unified layout

- Add Figlet text converter with font selection and history
- Add Pastel color palette generator and manipulation suite
- Add comprehensive Units converter with category-based logic
- Introduce AppShell with Sidebar and Header for navigation
- Modernize theme system with CSS variables and new animations
- Update project configuration and dependencies

components/ui/Card.tsx

@@ -0,0 +1,50 @@
+import * as React from 'react';
+import { cn } from '@/lib/utils/cn';
+
+const Card = React.forwardRef<HTMLDivElement, React.HTMLAttributes<HTMLDivElement>>(
+  ({ className, ...props }, ref) => (
+    <div
+      ref={ref}
+      className={cn('glass rounded-2xl text-card-foreground shadow-xl transition-all duration-300', className)}
+      {...props}
+    />
+  )
+);
+Card.displayName = 'Card';
+
+const CardHeader = React.forwardRef<HTMLDivElement, React.HTMLAttributes<HTMLDivElement>>(
+  ({ className, ...props }, ref) => (
+    <div ref={ref} className={cn('flex flex-col space-y-1.5 p-6', className)} {...props} />
+  )
+);
+CardHeader.displayName = 'CardHeader';
+
+const CardTitle = React.forwardRef<HTMLDivElement, React.HTMLAttributes<HTMLDivElement>>(
+  ({ className, ...props }, ref) => (
+    <div ref={ref} className={cn('font-semibold leading-none tracking-tight', className)} {...props} />
+  )
+);
+CardTitle.displayName = 'CardTitle';
+
+const CardDescription = React.forwardRef<HTMLDivElement, React.HTMLAttributes<HTMLDivElement>>(
+  ({ className, ...props }, ref) => (
+    <div ref={ref} className={cn('text-sm text-muted-foreground', className)} {...props} />
+  )
+);
+CardDescription.displayName = 'CardDescription';
+
+const CardContent = React.forwardRef<HTMLDivElement, React.HTMLAttributes<HTMLDivElement>>(
+  ({ className, ...props }, ref) => (
+    <div ref={ref} className={cn('p-6 pt-0', className)} {...props} />
+  )
+);
+CardContent.displayName = 'CardContent';
+
+const CardFooter = React.forwardRef<HTMLDivElement, React.HTMLAttributes<HTMLDivElement>>(
+  ({ className, ...props }, ref) => (
+    <div ref={ref} className={cn('flex items-center p-6 pt-0', className)} {...props} />
+  )
+);
+CardFooter.displayName = 'CardFooter';
+
+export { Card, CardHeader, CardFooter, CardTitle, CardDescription, CardContent };