fix(library): show full photo in each grid thumb (square + contain)

Library thumbs were locked to 4:3 with object-fit: cover, so portrait
photos got their top and bottom crop-fitted off. Switching to 1:1
cells with object-fit: contain — full photo always visible, grid still
uniform, portrait and landscape both get symmetric letterbox bars.

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

frontend/src/views/LibraryView.vue

@@ -584,9 +584,12 @@ async function doDelete() {
     gap: var(--space-2);
   }
 
+  // Square cells with object-fit: contain so both portrait and landscape
+  // photos render in full (no aggressive crop); grid stays uniform; aspect
+  // mismatches show as symmetric letterbox bars top/bottom or left/right.
   &__thumb {
     position: relative;
-    aspect-ratio: 4/3;
+    aspect-ratio: 1/1;
     border-radius: var(--radius-sm);
     overflow: hidden;
     background: var(--color-surface-2);
@@ -595,7 +598,7 @@ async function doDelete() {
   &__img {
     width: 100%;
     height: 100%;
-    object-fit: cover;
+    object-fit: contain;
     display: block;
   }