Fix: Krea-Thumbnails mit fester Höhe statt scrollDown-Listener

- _scrollOnImages() komplett entfernt (verursachte ungewolltes Runterscrollen)
- .krea-ref: feste Höhe 240px + min-width 240px + Placeholder-Hintergrund
- .krea-thumb: width/height 100% mit object-fit contain
- Browser reserviert Platz vor dem Laden → kein Layout-Shift

wwwroot/js/ui.js

@@ -79,16 +79,6 @@ function scrollDown() {
   });
 }
 
-function _scrollOnImages(container) {
-  var imgs = container.querySelectorAll('img');
-  for (var i = 0; i < imgs.length; i++) {
-    if (!imgs[i].complete) {
-      imgs[i].addEventListener('load', scrollDown);
-      imgs[i].addEventListener('error', scrollDown);
-    }
-  }
-}
-
 function esc(s) {
   const d = document.createElement('div');
   d.textContent = s;
@@ -244,7 +234,6 @@ function addAssistantBubble(text, timestamp = '', messageId = null, isMarked = f
   if (messageId) div.dataset.messageId = messageId;
   div.innerHTML = renderMarkdown(text);
   wrapKreaGalleries(div);
-  _scrollOnImages(div);
   _addReplyButton(div);
   _addMarkButton(div, messageId, isMarked);
   chatEl().appendChild(div);
@@ -310,7 +299,6 @@ function endStreamBubble() {
     else {
       _streamDiv.innerHTML = renderMarkdown(_streamText);
       wrapKreaGalleries(_streamDiv);
-      _scrollOnImages(_streamDiv);
     }
   }
   _streamDiv = null;