fix(home): preview locks aspect to panel dims + object-fit so it never overflows

The large FrameCard preview let the <img> drive height (`flex: 0 0
auto`, `width: auto`, `max-*: 100%`). On wide-container layouts and on
the new V2 1200×1600 dimensions the image's intrinsic size leaked
past the card, and the max-width/max-height combo can drop aspect
ratio in some browsers.

Now: the preview container locks its `aspect-ratio` to
`panelDims(model, orientation)` — same source of truth that drives the
empty-placeholder shape — and the <img> fills the container with
`object-fit: contain`. Container shape is stable whether or not the
thumbnail has loaded; image always scales to fit, portrait or
landscape device, narrow or wide phone column.

emptyAspectStyle no longer needs to carry aspect (parent already has
it); empty-preview placeholder fills 100% of the parent now.

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-DHJU4XGZ.js"></script>
+    <script type="module" crossorigin src="/build/assets/index-RZqoO867.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>