🎨 Palette: [UX improvement] Add aria-hidden to decorative SVGs (#70)

* Added aria-hidden="true" to decorative SVG icons within interactive elements (buttons, links) in Lightbox, ThemeToggle, Footer, BackLink, and MapView.
* Added role="alert" and aria-live="polite" to the MapView loading indicator.
* Documented learning in .Jules/palette.md

Co-authored-by: google-labs-jules[bot] <161369871+google-labs-jules[bot]@users.noreply.github.com>

components/BackLink.tsx

@@ -14,6 +14,7 @@ export function BackLink({ href, label }: BackLinkProps) {
   return (
     <Link href={href} className="album-header__back" aria-label={`Back to ${label}`}>
       <svg
+        aria-hidden="true"
         viewBox="0 0 24 24"
         fill="none"
         stroke="currentColor"