Editable Invoice IDs for Group Invoices

We've enhanced group invoice management with two key improvements:

What's New

1. Editable Invoice ID — You can now manually edit the Invoice ID on group invoices

2. Randomised ID generation — Group invoices now include 5 randomised alphanumeric characters in the Invoice ID, preventing duplicate conflicts

Why This Matters

Previously, group invoices could default to the same ID pattern, which caused blocking issues during invoice generation. This update resolves that limitation.

Note: These changes apply to group invoices only — individual client invoice generation remains unchanged.