🎨 Palette: Add skip to main content link for keyboard accessibility

[0m364]

💡 What: Added a visually hidden "Skip to main content" link that appears on keyboard focus, alongside a target main container setup with id="main-content" and tabindex="-1".

🎯 Why: To improve navigation for users relying on keyboard inputs or screen readers, allowing them to bypass redundant navigation links and access the primary content immediately on each page without friction.

📸 Before/After: See attached Playwright screenshots of skip_link_focused.png.

♿ Accessibility: This implements a core WCAG best practice by ensuring main content sections can receive programmatic focus via a valid skip link, greatly improving navigational accessibility.

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PR created automatically by Jules for task 3173780419545834644 started by @0m364

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