feat(showcase): IR-parity hover animation on masonry thumbnails

FC already matched IR's staggered entry fade-in; this adds the missing
piece — hover zoom (scale 1.03) + brighten (1.1) on each thumbnail, with
overflow:hidden so the scaled image clips to the rounded card. Disabled
under prefers-reduced-motion.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

frontend/src/components/discovery/MasonryGrid.vue

@@ -100,10 +100,17 @@ onUnmounted(() => observer && observer.disconnect())
 .fc-masonry__item {
   display: block; padding: 0; border: 0; background: none;
   cursor: pointer; width: 100%;
+  overflow: hidden; border-radius: 4px;
 }
 .fc-masonry__item img {
-  width: 100%; height: auto; display: block; border-radius: 4px;
+  width: 100%; height: auto; display: block;
   background: rgb(var(--v-theme-surface-light));
+  /* IR-parity hover: zoom + brighten the thumbnail (style.css ~1772). */
+  transition: transform 0.3s ease, filter 0.3s ease;
+}
+.fc-masonry__item:hover img {
+  transform: scale(1.03);
+  filter: brightness(1.1);
 }
 .fc-masonry__sentinel {
   display: flex; justify-content: center; padding: 32px 0; min-height: 60px;
@@ -127,5 +134,7 @@ onUnmounted(() => observer && observer.disconnect())
     animation: none;
     opacity: 1;
   }
+  .fc-masonry__item img { transition: none; }
+  .fc-masonry__item:hover img { transform: none; }
 }
 </style>