🎨 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/ThemeToggle.tsx

@@ -63,6 +63,7 @@ export function ThemeToggle() {
       {theme === 'dark' ? (
         // Sun icon
         <svg
+          aria-hidden="true"
           width="16"
           height="16"
           viewBox="0 0 24 24"
@@ -85,6 +86,7 @@ export function ThemeToggle() {
       ) : (
         // Moon icon
         <svg
+          aria-hidden="true"
           width="16"
           height="16"
           viewBox="0 0 24 24"