Email templates: populate $item / $description (or add $line_item_summary) for invoice emails

Summary Invoice email templates expose $item and $description (and $product.*) via HtmlEngine, but they are empty stubs used as PDF column labels. Putting them in an invoice email body shows blank — not the line-item product key or notes. Operators who want the email to say what the charge is for currently must rely on $public_notes (works) and operational discipline to fill public notes on every send/recurring. Request Please either: 1. Populate $description / $item (or $product.description / $product.product_key) from the invoice’s first line item for email rendering, or 2. Add a dedicated variable such as $line_item_summary / $first_item_notes that lists product_key + notes (+ amount) for use in email_subject_invoice / email_template_invoice. Optional: a company setting “Include line items in invoice emails.” Why it matters Clients often only read the email. Subject/body with number + amount alone (“New InvoiceR2026-1376 for $11.25”) does not explain the charge. The portal/…