- Upgraded all plain `require` to `require_once` across 172 api/engine
and api/engine_report files to prevent class-redeclaration errors
- Added issue button, issue_invoice() with GL toastr, and delete_invoice()
to expense/manage_purchase_invoice.php, bringing it in line with
po/manage_purchase_invoice.php
- Added can_delete role guard (admin/owner only) to trash icons on
revenue/invoice.php and expense/purchase_invoice.php, matching the
existing pattern in finance/receipt.php and finance/payment.php
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
