🎨 Palette: Add Semantic Roles and Spacebar Accessibility to Modal Triggers

[0m364]

💡 What: Added role="button" and aria-haspopup="dialog" to the a#sitrep-btn modal triggers across HTML pages, and implemented spacebar keydown handling in modal.js with e.preventDefault().
🎯 Why: Using anchor tags as buttons without proper ARIA roles misleads screen readers. Additionally, native anchor tags do not respond to the 'Space' key, which is expected behavior for buttons. Pressing 'Space' would scroll the page.
📸 Before/After: N/A (Non-visual behavior/accessibility change). Tested using playwright script verifying 'Space' triggers the modal.
♿ Accessibility: Ensures screen readers announce the element as a dialog-triggering button and allows keyboard-only users to activate the modal using standard button interaction (Spacebar).

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PR created automatically by Jules for task 8144279338942367715 started by @0m364

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