Improve user experience by providing colored notifications for operations

Modify toast notifications to display success messages in green and errors in red using the "variant" property in Administration.tsx, NewSaleForm.tsx, and SalesHistory.tsx.

Replit-Commit-Author: Agent
Replit-Commit-Session-Id: dec54137-d5a2-4406-8ad4-5f2f9fb110bf
Replit-Commit-Screenshot-Url: https://storage.googleapis.com/screenshot-production-us-central1/0715008c-7244-40f4-befc-26c014852236/5aef45ab-dd7f-4d72-856e-de1c85394516.jpg

client/src/components/NewSaleForm.tsx

@@ -82,6 +82,7 @@ export default function NewSaleForm() {
       toast({
         title: "Vente enregistrée",
         description: "La vente a été enregistrée avec succès",
+        variant: "success",
       });
       form.reset({
         vendeur: '',