refactor: streamline toast system and harmonize UI across tools

- Migrate all toast notifications to sonner and remove custom ToastProvider
- Align Card and TextInput styling across Figlet and Pastel (rounded-lg, border-based)
- Fix build error by removing non-existent export in lib/units/index.ts
- Clean up unused Figlet components and constants

app/(app)/figlet/page.tsx

@@ -2,12 +2,16 @@ import { FigletConverter } from '@/components/figlet/FigletConverter';
 
 export default function FigletPage() {
   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">Figlet UI</h1>
-        <p className="text-muted-foreground italic">ASCII Art Text Generator with 373 Fonts</p>
+    <div className="min-h-screen py-12">
+      <div className="max-w-7xl mx-auto px-8 space-y-8">
+        <div>
+          <h1 className="text-4xl font-bold mb-2">Figlet ASCII</h1>
+          <p className="text-muted-foreground">
+            ASCII Art Text Generator with 373 Fonts
+          </p>
+        </div>
+        <FigletConverter />
       </div>
-      <FigletConverter />
     </div>
   );
 }