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)/units/page.tsx

@@ -0,0 +1,13 @@
+import MainConverter from '@/components/units/converter/MainConverter';
+
+export default function UnitsPage() {
+  return (
+    <div className="p-4 sm:p-8 max-w-7xl mx-auto">
+      <div className="mb-8">
+        <h1 className="text-3xl font-bold mb-2">Units Converter</h1>
+        <p className="text-muted-foreground italic">Smart unit converter with 187 units across 23 categories</p>
+      </div>
+      <MainConverter />
+    </div>
+  );
+}