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

components/providers/Providers.tsx

@@ -4,7 +4,6 @@ import { QueryClient, QueryClientProvider } from '@tanstack/react-query';
 import { Toaster } from 'sonner';
 import { useState } from 'react';
 import { ThemeProvider } from './ThemeProvider';
-import { ToastProvider } from '@/components/ui/Toast';
 
 export function Providers({ children }: { children: React.ReactNode }) {
   const [queryClient] = useState(
@@ -21,12 +20,10 @@ export function Providers({ children }: { children: React.ReactNode }) {
 
   return (
     <ThemeProvider>
-      <ToastProvider>
-        <QueryClientProvider client={queryClient}>
-          {children}
-          <Toaster position="top-right" richColors />
-        </QueryClientProvider>
-      </ToastProvider>
+      <QueryClientProvider client={queryClient}>
+        {children}
+        <Toaster position="top-right" richColors />
+      </QueryClientProvider>
     </ThemeProvider>
   );
 }