🎨 Palette: Accessible Anchor Buttons

[0m364]

💡 What: Added proper semantic attributes (role="button", aria-haspopup="dialog") and a JavaScript spacebar event handler to the "OSINT" anchor tags (#sitrep-btn) across the site. Also added the missing link to the index.html navbar.
🎯 Why: Anchor tags (<a> with href="#") used to trigger modals break accessibility expectations. Native anchors trigger on Enter but not on Space (which just scrolls the page), and screen readers announce them as links instead of actionable buttons.
📸 Before/After: Visually identical. A screenshot of the modal successfully opening has been provided in the pre-commit checks.
♿ Accessibility: Screen readers will now correctly announce the link as a button that opens a dialog. Keyboard users can now intuitively trigger the modal using the Spacebar without the page suddenly scrolling away.

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PR created automatically by Jules for task 9816705825757504987 started by @0m364

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