Fix workshop reader accessibility semantics and QA screenshot publishing

[Copilot]

The workshop single-page reader rendered no top-level heading, skipped heading levels by promoting page titles to <h4> inside <summary>, and emitted task-list checkboxes without accessible names. The Playwright QA workflow also referenced local screenshot paths instead of publishing embeddable assets in issues.

• Reader heading semantics

  • Render each workshop page title as a visible page-level <h1> instead of a <h4> in the disclosure summary.
  • Keep the disclosure summary non-visual so the reader retains page-switching behavior without polluting the heading outline.
  • Preserve valid heading progression across each rendered workshop section.

• Task list accessibility

  • Derive an accessible name from each checklist item’s rendered text.
  • Apply that text as aria-label on generated task-list checkboxes.

• HTML safety

  • Centralize text flattening/escaping for generated heading and checkbox attributes to avoid unsafe interpolation.

• QA workflow screenshot assets

  • Add upload-asset safe output to the Playwright QA workflow.
  • Update the workflow prompt so each finding uploads its screenshot and embeds the returned asset URL directly in the issue/comment body.

Example of the generated checkbox markup after this change:

<li class="task-list-item">
  <input
    class="task-list-item-checkbox"
    disabled=""
    type="checkbox"
    aria-label="You have a GitHub account with access to GitHub Codespaces">
  You have a GitHub account with access to GitHub Codespaces
</li>

• Fixes [workshop-playwright-qa] __root__: 3 QA finding(s) — accessibility #1732