fix header levels in example code in README.md

[brandonzylstra]

If I understood the intention of the example, I think this is what was meant.

[Copilot]

Pull request overview

This PR attempts to fix the expected HTML output in the README.md example by changing the heading tags to match their corresponding aria-level attributes (e.g., <h1 aria-level="1"> instead of <h3 aria-level="1">). However, this creates a critical discrepancy with the actual component implementation.

Key Issue:

• The Heading.astro component (shown in the README and confirmed in demo/src/components/Heading.astro) always renders an <h3> tag with a dynamic aria-level attribute
• The "corrected" output now shows varying heading tags (<h1>, <h2>, <h3>, <h4>) that the component cannot actually produce

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[Copilot]

The corrected HTML output shows varying heading tags (h1, h2, h3, h4) that match their aria-level attributes. However, the Heading.astro component implementation shown above (line 65) always renders an h3 tag with a dynamic aria-level attribute. This creates a discrepancy: the actual output would be all h3 tags with different aria-level values, not different heading tags. Either the component implementation should be updated to dynamically select the heading tag (e.g., using a dynamic element or conditional rendering), or the expected output should show h3 tags consistently to accurately reflect what the component actually produces.