🎨 Palette: Add skip-to-main content links

[0m364]

💡 What: Added a "Skip to main content" link to all HTML pages (index.html, contact.html, products.html, concepts.html) that allows keyboard users to bypass the site header and jump directly to the primary content. The link is visually hidden off-screen using transform: translateY(-100%) and becomes visible on :focus.

🎯 Why: Without a skip link, keyboard-only users (and often screen reader users) are forced to repeatedly Tab through all navigation elements on every single page load before reaching the actual content. This is a crucial WCAG accessibility requirement.

📸 Before/After:

• Before: Pressing Tab on page load focuses the first header link.
• After: Pressing Tab on page load focuses the new "Skip to main content" link, which slides down gracefully from the top of the screen. Pressing Enter immediately shifts focus and scroll position to the main content area.

♿ Accessibility:

• Added <a href="#main-content" class="skip-link">Skip to main content</a> as the first focusable element.
• Updated <main class="container"> to <main id="main-content" class="container" tabindex="-1">. The tabindex="-1" is essential to ensure the <main> element can receive programmatic focus when the skip link is activated, fixing a common issue where focus gets lost in some browsers.
• Added .skip-link utility class utilizing transform instead of display: none or absolute top positioning for robust cross-browser and varied-screen-size behavior.

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PR created automatically by Jules for task 17139637552377216615 started by @0m364

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