chore(fast-html): use @microsoft/fast-build to build ref fixture

[janechu]

Pull Request

📖 Description

Adds the ref test fixture to @microsoft/fast-html and generates its index.html using @microsoft/fast-build, consistent with the other fixtures (attribute, binding, event).

The ref fixture covers f-ref attribute directives, which bind a reference to a DOM element in a FAST template (e.g. <video f-ref="{video}"></video>). Because f-ref is client-side only, @microsoft/fast-build strips it from the rendered Declarative Shadow DOM and preserves only the data-fe-c hydration binding count so the FAST runtime can allocate the correct number of binding slots.

🎫 Issues

No open issues directly addressed.

📑 Test Plan

• npm run build:fixtures in packages/fast-html runs cleanly and regenerates ref/index.html — f-ref is stripped from shadow DOM output, data-fe-c-0-1 binding annotation is preserved.
• All other fixture outputs (attribute, binding, event) are unchanged.

✅ Checklist

General

• I have included a change request file using $ npm run change
• I have added tests for my changes.
• I have tested my changes.
• I have updated the project documentation to reflect my changes.
• I have read the CONTRIBUTING documentation and followed the standards for this project.

⏭ Next Steps

• Add a Playwright spec file (ref.spec.ts) covering hydration of the f-ref fixture to verify client-side element reference assignment after SSR.

[Copilot]

Pull request overview

Updates the @microsoft/fast-html test fixture set by adding a ref fixture and wiring it into the existing @microsoft/fast-build-based fixture build pipeline, aligning it with attribute, binding, and event.

Changes:

• Adds ref fixture inputs (entry.html, templates.html, state.json) for @microsoft/fast-build.
• Regenerates ref/index.html using @microsoft/fast-build output plus template injection.
• Includes ref in packages/fast-html/scripts/build-fixtures.js so npm run build:fixtures builds it.

Reviewed changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
packages/fast-html/test/fixtures/ref/templates.html	Adds declarative template using f-ref for the ref fixture.
packages/fast-html/test/fixtures/ref/state.json	Adds state input for the ref fixture build (empty state).
packages/fast-html/test/fixtures/ref/entry.html	Adds build entry HTML for the ref fixture (matches other buildable fixtures).
packages/fast-html/test/fixtures/ref/index.html	Updates generated fixture output to the fast-build produced HTML + injected <f-template> declarations.
packages/fast-html/scripts/build-fixtures.js	Adds ref to the list of fixtures built via @microsoft/fast-build.
change/@microsoft-fast-html-ref-eb80fd68-6df1-46bc-848d-f59cd9be4b49.json	Records the change request for the @microsoft/fast-html package.