Fix HTML rendering of relationship variables in CiceroMark

[Aradhana2803]

Fix HTML rendering of relationship variables in CiceroMark

Related to accordproject/template-playground#13

Summary

Relationship-typed CiceroMark variables were rendered in HTML as quoted
resource: strings instead of a readable identifier. This PR fixes the
HTML rendering logic so relationship variables display correctly.[TemplateMark not rendering relationships "resource" data #13]

Changes

• Update ToHtmlStringVisitor to detect relationship variables via elementType
• Render a clean relationship identifier instead of the raw serialized value
• Preserve existing rendering behavior for primitive variable types

Flags

• No breaking changes
• Change is limited to HTML rendering only (CiceroMark JSON unchanged)

Screenshots or Video

Not applicable — behavior verified via existing HtmlTransformer test suite.

Author Checklist

• Ensure you provide a DCO sign-off for your commits using the --signoff option of git commit
• Vital features and changes captured in unit and/or integration tests
• Commits messages follow AP format
• Extend the documentation, if necessary
• Merging to main from fork:branchname

[Aradhana2803]

This PR fixes the issue reported in template-playground#13 where relationship-typed CiceroMark variables were rendered as quoted resource: strings instead of a readable identifier. HTML rendering now preserves the identifier cleanly, while keeping other variable types unchanged.Verified that Party relationship variables now render clean identifiers in HTML
without quotes. All existing HtmlTransformer tests pass.