feat(home): full-size frame card; horizontal carousel for multi-frame setups

Reverts the 240px preview cap — frames render at their natural device aspect
again. Single-frame layout unchanged.

For multi-frame setups, replaces the compact stack with a horizontal
scroll-snap carousel: one large card per slide, full-bleed to the viewport
edges, with dot navigation below that tracks the active slide and supports
tap-to-jump. Native CSS scroll-snap drives the swipe gesture; no extra JS
gesture library.

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

frontend/src/components/FrameCard.vue

@@ -168,23 +168,18 @@ const statusText = computed(() => {
     opacity: 0.6;
   }
 
-  // ── Large (single device) ────────────────────────────────────────────────
-  // Portrait frames have aspect 3:5 — at full mobile width (~360px) that would
-  // be 600px tall and totally dominate the screen. Cap so the card stays
-  // phone-friendly while still showing the photo at the frame's real shape.
+  // ── Large (single device or carousel slide) ──────────────────────────────
   &--large &__preview {
     background: var(--color-surface-2);
     display: flex;
     align-items: center;
     justify-content: center;
-    max-height: min(240px, 30dvh);
-    overflow: hidden;
   }
 
   &--large &__img {
     width: 100%;
     height: 100%;
-    object-fit: contain;
+    object-fit: cover;
   }
 
   &--large &__empty-preview {