fix(frame-card): cap portrait preview to 40dvh so cards stop dominating

Portrait frames (3:5 aspect) at full card width were rendering 600px tall
and pushing the body well off-screen. Cap preview max-height at 40dvh and
switch the img sizing to max-width/max-height: 100% with auto width/height
— photo scales to fit inside the capped preview at its native aspect, with
narrow grey side bars filling the leftover horizontal space. Landscape
frames are short enough that the cap never engages.

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

frontend/src/components/FrameCard.vue

@@ -186,16 +186,25 @@ const statusText = computed(() => {
     height: 100%;
   }
 
+  // Cap the preview height so portrait frames (3:5) don't blow past half
+  // the viewport. Landscape frames (5:3) at full card width are short enough
+  // that the cap never engages. The photo is centered within the preview;
+  // portrait shots get a thin grey bar on each side instead of stretching.
   &--large &__preview {
     flex: 0 0 auto;
     background: var(--color-surface-2);
-    display: block;
+    display: flex;
+    align-items: center;
+    justify-content: center;
     overflow: hidden;
+    max-height: 40dvh;
   }
 
   &--large &__img {
     display: block;
-    width: 100%;
+    max-width: 100%;
+    max-height: 100%;
+    width: auto;
     height: auto;
   }