Form pattern for asking about gender or sex

# Opportunity

A standard for how to ask for sex/gender in an inclusive way (if it's absolutely necessary in a form) that defaults to optional.

Explore common identity questions such as:
- Pronoun
- Title
- Marital status
- Gender identity
- Sexual orientation
- Sex assigned at birth
- Name on X document

Consider other types of equality information https://design-system.service.gov.uk/patterns/equality-information/

# Links
- https://www.canada.ca/en/women-gender-equality/free-to-be-me/making-programs-services-inclusive.html
- https://miro.com/app/board/uXjVLzrzVyo=/
- https://github.com/alphagov/govuk-design-system-backlog/issues/69
- https://design-system.service.gov.uk/patterns/gender-or-sex/
- https://www.canada.ca/en/treasury-board-secretariat/corporate/reports/summary-modernizing-info-sex-gender.html
- https://medium.com/pew-research-center-decoded/adapting-how-we-ask-about-the-gender-of-our-survey-respondents-77b0cb7367c0
- https://docs.google.com/presentation/d/1ZSp1OP_Oi_R_1Vw3hOeZT9IZO2RBAy_aFdJbMzJuPNk/edit#slide=id.g31d438771d_0_665
- https://docs.google.com/document/d/1zoBWalIDHX2L5pyfnS51JHHuSFVb3e5MxfNmttPXKX4/edit?tab=t.0#heading=h.w8iy961mnol4
- https://docs.google.com/document/d/139eFDyNRJe9opj9LEkxzx1QAEMIysfk5sY2feBwuhKA/edit?tab=t.0

Start by reviewing the linked GOV.UK and Canadian guidance, along with the existing discussion links, to understand the proposed inclusive form patterns. Define the scope and intended outcome before locating implementation entry points; done should be a decided, documented pattern covering the listed identity questions and optionality.

Written by the indexing model from the issue text.