Add Support for Custom Invoice Number Prefixes

🔍 Problem Statement

Currently, the invoice numbers generated by Pelcro are long, system-generated numeric strings with no option to customize or add a prefix. This makes them difficult for businesses to associate with their brand or internal accounting conventions.

💡 User Story

As a business, I want to add a custom prefix or shorten the invoice number format, so that invoices are easier to identify, organize, and align with my brand or financial reporting standards.