🎨 Palette: Improve README heading accessibility

[google-labs-jules]

💡 What:
Updated the main heading in README.md from a level-2 heading (##) to a level-1 heading (#).

🎯 Why:
Starting a document with a single, top-level heading (<h1>) is a fundamental accessibility principle. It provides a clear and semantic entry point for the entire document, which allows users of assistive technologies, like screen readers, to quickly understand the page's purpose and navigate its structure more efficiently. The previous use of a level-2 heading broke this logical hierarchy.

♿ Accessibility:
This change directly improves the experience for screen reader users by establishing a correct and predictable document structure. It ensures the main title is properly identified, making navigation more intuitive.

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PR created automatically by Jules for task 5488635462325924370 started by @Moohan

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