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/Stats.tsx

@@ -48,7 +48,7 @@ export default function Stats() {
               whileHover={{ y: -5 }}
             >
               <motion.div
-                className="inline-flex items-center justify-center w-12 h-12 mb-4 rounded-xl bg-gradient-to-br from-purple-500/20 to-cyan-500/20 text-purple-400"
+                className="inline-flex items-center justify-center w-12 h-12 mb-4 rounded-xl bg-primary/10 text-primary"
                 whileHover={{ scale: 1.1, rotate: 5 }}
                 transition={{ type: 'spring', stiffness: 300 }}
               >
@@ -57,7 +57,7 @@ export default function Stats() {
               <div className="text-4xl font-bold mb-2 bg-clip-text text-transparent bg-gradient-to-r from-purple-400 to-cyan-400">
                 {stat.number}
               </div>
-              <div className="text-gray-400 text-base font-medium">
+              <div className="text-muted-foreground text-base font-medium">
                 {stat.label}
               </div>
             </motion.div>