🎨 Palette: Add skip to main content link

[0m364]

💡 What: Added a visually hidden "Skip to main content" link to the top of all pages (index.html, concepts.html, products.html, contact.html).
🎯 Why: Keyboard and screen reader users have to tab through all navigation links on every page load before reaching the main content. This bypass link improves efficiency and usability for those relying on keyboard navigation.
📸 Before/After: Visuals verified locally via Playwright screenshots. The link is invisible unless focused, adhering to the site's design until needed.
♿ Accessibility: Ensures WCAG compliance for bypassing blocks of content (Success Criterion 2.4.1). Added id="main-content" to the <main> tags to provide an anchor target for the skip link. Updated .Jules/palette.md with learning.

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PR created automatically by Jules for task 2943715202024785547 started by @0m364

[google-labs-jules]

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