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

app/(app)/pastel/layout.tsx

@@ -0,0 +1,11 @@
+export default function PastelLayout({
+  children,
+}: Readonly<{
+  children: React.ReactNode;
+}>) {
+  return (
+    <div className="p-4 sm:p-8 max-w-7xl mx-auto">
+      {children}
+    </div>
+  );
+}