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

[ELO2026X]

💡 What

Added a "Skip to main content" link to the application layout that is visually hidden but appears when navigated to via keyboard. Updated the main content area to be a semantic <main> tag that correctly handles receiving focus.

🎯 Why

Keyboard-only users and those using screen readers often have to navigate through the same repetitive navigation links (like the sidebar) on every page interaction. A "skip link" provides a crucial shortcut to jump directly to the primary content of the application.

📸 Before/After

Before: Keyboard users must tab through the entire sidebar to reach the main content.
After: The first tab press from the top of the document reveals a "Skip to main content" button. Pressing enter instantly focuses the main content area.

(A Playwright verification script was run to visually verify the link appears on focus, and that activating it successfully focuses the main content area.)

♿ Accessibility

• Added a href="#main-content" link that is hidden visually using standard tailwind utilities (sr-only) but visible on focus (focus-visible:not-sr-only).
• Converted the primary content <div> in ContentView.tsx to a semantic <main> element.
• Added id="main-content" to act as the target for the skip link.
• Added tabIndex={-1} and focus:outline-none to the <main> element. This ensures the container can receive programmatic focus when the skip link is clicked, allowing subsequent keyboard navigation to flow naturally from that point, while preventing an ugly focus ring from appearing around the entire content block.

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PR created automatically by Jules for task 13516408964087902137 started by @ELO2026X

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