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>

public/build/index.html

@@ -14,7 +14,7 @@
     <meta name="mobile-web-app-capable" content="yes" />
     <meta name="apple-mobile-web-app-status-bar-style" content="default" />
     <meta name="apple-mobile-web-app-title" content="pictureFrame" />
-    <script type="module" crossorigin src="/build/assets/index-RZqoO867.js"></script>
+    <script type="module" crossorigin src="/build/assets/index-Bx9Y0zPK.js"></script>
     <link rel="modulepreload" crossorigin href="/build/assets/_plugin-vue_export-helper-BNDVmFr7.js">
     <link rel="stylesheet" crossorigin href="/build/assets/index-BlLBHR1q.css">
   </head>