feat(photoswipe): animate keyboard arrow navigation in lightbox

PhotoSwipe's goTo() moves slides instantly (no spring animation unlike
swipe). Intercepts keydown in capture phase, sets a CSS transition and
forces a reflow before PhotoSwipe moves the container, so the browser
animates from the old position to the new one. Cleans up on close.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Vgmzx8VTTTmCskSpQtsLTr

themes/intotheeast/templates/dailies.html.twig

@@ -110,6 +110,17 @@ const lightbox = new PhotoSwipeLightbox({
     children: 'a.journal-photo-slide',
     pswpModule: () => import('https://cdn.jsdelivr.net/npm/photoswipe@5/dist/photoswipe.esm.min.js')
 });
+lightbox.on('afterOpen', function () {
+    var container = lightbox.pswp.element.querySelector('.pswp__container');
+    function onKey(e) {
+        if (e.key !== 'ArrowLeft' && e.key !== 'ArrowRight') return;
+        container.style.transition = 'transform 0.35s cubic-bezier(0.4, 0, 0.22, 1)';
+        container.getBoundingClientRect();
+        setTimeout(function () { container.style.transition = ''; }, 400);
+    }
+    document.addEventListener('keydown', onKey, true);
+    lightbox.pswp.on('close', function () { document.removeEventListener('keydown', onKey, true); });
+});
 lightbox.init();
 
 /* Per-strip: dot sync + expand button → tap the visible slide to trigger pswp */