PDF: Add {{quote.number}} as available variable in quote PDF filename field

We would like to be able to use {{quote.number}} as a variable in the quote PDF filename default field, so the quote number can be included automatically in the generated filename.

Use case:

We want filenames structured like "Offerte {{quote.number}} - {{quote.title}}.pdf" so files are easy to identify and sort without manual renaming.

Current situation:
The filename field does not list {{quote.number}} as an available variable, and testing confirms it does not resolve even though it is a valid quote property.