Alternative.images: array of urls, rendered as a Swiper card deck

image: Option<String> becomes images: Vec<String> (nothing in live
content used the old field). One url renders as the plain banner it
was; several become a swipeable cards-effect deck via Swiper Element
12.2.0, vendored into public/ (MIT) like prosekit-editor.js/yes.js
rather than pulled from a CDN - the bundle only loads on pages where
some alternative actually declares more than one image.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

style/main.css

@@ -270,6 +270,25 @@ main.not-found {
   margin-bottom: 1.1rem;
 }
 
+/* Sized down from full card width so the cards effect's fanned-out
+   neighbors stay inside the card - swiper positions slides absolutely,
+   so the container needs its own height. Before the bundle upgrades
+   the element (or without JS) slides stack as plain blocks; capping
+   the container height keeps that fallback from towering. */
+.alt-image-deck {
+  display: block;
+  width: min(100%, 22rem);
+  height: 14rem;
+  margin: 0 auto 1.1rem;
+  overflow: hidden;
+}
+
+.alt-image-deck .alt-image {
+  height: 100%;
+  max-height: none;
+  margin-bottom: 0;
+}
+
 .alt-card h2 {
   font-size: 1.3rem;
 }