🎨 Palette: Add 'Skip to main content' link

[ELO2026X]

💡 What: Added a 'Skip to main content' link in the root component and configured the main view container to be focusable programmatically.
🎯 Why: Enhances keyboard and screen-reader accessibility by allowing users to bypass repetitive navigation and jump directly to the primary 3D visualizer content.
📸 Before/After: Verified locally via Playwright screenshots (link remains visually hidden unless focused with a keyboard, revealing a prominent button at the top-left).
♿ Accessibility: Uses tabIndex={-1} and focus:outline-none on the main container to correctly receive focus without exposing an unnecessary visible outline, and employs robust Tailwind hiding (sr-only and focus-visible:not-sr-only) to avoid layout shifts.

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PR created automatically by Jules for task 2762929988127166399 started by @ELO2026X

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