feat(ui): add card hover preview element to collection page

ui/collection.html

@@ -19,5 +19,9 @@
             Collection.init();
         });
     </script>
+        <!-- Card Preview Popup (hover tooltip) -->
+    <div id="coll-card-preview" style="display:none; position:fixed; pointer-events:none; z-index:9999;">
+        <img id="coll-card-preview-img" src="" alt="Card preview" style="width:220px; border-radius:8px; box-shadow:0 8px 24px rgba(0,0,0,0.7);" />
+    </div>
 </body>
 </html>