Adds `role="dialog"`, `aria-modal="true"`, and `aria-label` to the `.overlay` container to improve screen reader accessibility. Also adds `aria-expanded` and `aria-controls` to the EXIF info toggle button, linking it to the newly ID'd `#exif-panel`.
Co-authored-by: google-labs-jules[bot] <161369871+google-labs-jules[bot]@users.noreply.github.com>