Feature Request: Add accountName and orderReference to billing-document template #11

Summary

The billing-document.ts template is missing two PEPPOL BIS 3.0 fields that would improve the invoice preview:

1. Account Name (BT-85) - Name of the bank account holder
2. Order Reference (BT-13) - Purchase order reference

1. Account Name (BT-85)

The PayeeFinancialAccount/Name field is parsed but not displayed in the template.

The payment section in templates/billing-document.ts shows iban, reference, and financialInstitutionBranch, but not accountName.

Suggested addition:

{{#accountName}}
  <p class="text-xs text-slate-500">Account: {{accountName}}</p>
{{/accountName}}

2. Order Reference (BT-13)

The Purchase Order Reference (cac:OrderReference/cbc:ID) is parsed in utils/parsing/invoice/from-xml.ts but not displayed in the template.

Currently only buyerReference (BT-10) is shown in the header.

Suggested addition:

{{#orderReference}}
  <span>&bull;</span>
  <span>Order reference: {{orderReference}}</span>
{{/orderReference}}

Why this matters

Both fields are part of PEPPOL BIS 3.0:

• BT-85 (Account Name) helps verify the correct recipient of payment
• BT-13 (Order Reference) is commonly used by businesses to link invoices to purchase orders

The data is already being parsed - it just needs to be added to the template for display.