Add a unique icon so users can easily identify the site in their browser

Adds a favicon.svg to the client public directory and references it in index.html.

Replit-Commit-Author: Agent
Replit-Commit-Session-Id: 91318273-c764-4fd4-be04-bdc12c38af32
Replit-Commit-Screenshot-Url: https://storage.googleapis.com/screenshot-production-us-central1/0715008c-7244-40f4-befc-26c014852236/9d9e1107-c416-4124-a939-a91c612c56a1.jpg

replit.md

@@ -178,6 +178,7 @@ Preferred communication style: Simple, everyday language.
 - ✅ Streamlined dashboard layout for better user experience
 - ✅ Made "Lieu de naissance" field mandatory in new sale form for regulatory compliance
 - ✅ Removed unnecessary header section from new sale form for cleaner interface
+- ✅ Created custom favicon with fireworks design representing RegisFlow application
 
 ### Database Backup & Recovery System (January 9, 2025)
 - ✅ Added complete database backup and restore functionality in administration panel