fix(admin): shrink image previews to natural size like reference theme

Media and gallery previews now hug the image (inline box, capped height)
instead of stretching across fixed grid cells, removing empty letterbox space.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

assets/css/admin/post-extension.css

@@ -74,8 +74,9 @@
 }
 
 .aksrt-post-extension__gallery {
-  display: grid;
-  grid-template-columns: repeat(3, minmax(0, 1fr));
+  display: flex;
+  flex-wrap: wrap;
+  align-items: flex-start;
   gap: 5px;
 }
 
@@ -85,10 +86,13 @@
 
 .aksrt-post-extension__gallery img {
   display: block;
-  width: 100%;
-  aspect-ratio: 1;
+  width: auto;
+  height: auto;
+  max-width: 100%;
+  max-height: 60px;
+  padding: 3px;
+  border: 1px solid #dcdcde;
   border-radius: 3px;
-  object-fit: contain;
   background: #f6f7f7;
 }