Create guide and evals for the html use case

[chrome-devrel-infra]

Action-oriented guidelines for modern HTML architecture, semantics, native interactive APIs (Dialog, Popover, Details), focus management, and resource prioritization. Use this guide when structuring web documents, implementing native overlays, or optimizing resource loading order.

Affected web-feature IDs:

Use case subdir: guides/html/html

Required files:

• Use case metadata (guide.md frontmatter)
• demo.html
• Use case guidance (guide.md)
• expectations.md
• tasks/task.md
• negative-demo.html
• grader.ts