fix(home): floor frame-card preview to 50dvh so landscape frames feel hero-sized

The natural 5:3 aspect ratio renders landscape devices as a ~200px-tall strip
on a phone — too small now that the carousel gives each slide the full
viewport. Set min-height: 50dvh so landscape preview is at least half the
screen tall, with object-fit: contain letterboxing the photo. Portrait
frames (3:5) still drive their height from the natural aspect ratio, since
that's already taller than the 50dvh floor.

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

frontend/src/components/FrameCard.vue

@@ -169,17 +169,21 @@ const statusText = computed(() => {
   }
 
   // ── Large (single device or carousel slide) ──────────────────────────────
+  // Floor the preview to a healthy chunk of the viewport so landscape frames
+  // (5:3) don't render as a thin strip. Portrait frames (3:5) keep their
+  // natural aspect — taller still wins.
   &--large &__preview {
     background: var(--color-surface-2);
     display: flex;
     align-items: center;
     justify-content: center;
+    min-height: 50dvh;
   }
 
   &--large &__img {
     width: 100%;
     height: 100%;
-    object-fit: cover;
+    object-fit: contain;
   }
 
   &--large &__empty-preview {