feat(agents): show images in sent messages (#439)

Images sent to an agent were dropped from the conversation: the user message kept only text and file chips. User entries now record their images and show them as thumbnails that open full size; composer thumbnails open the same preview. Editing a sent message keeps its images (removable) and rerunning from it sends them again.

src/features/agents/Composer.module.css

@@ -72,6 +72,15 @@
   box-shadow: inset 0 0 0 1px var(--border);
   overflow: hidden;
 }
+.previewImage {
+  display: block;
+  width: 100%;
+  height: 100%;
+  padding: 0;
+  border: 0;
+  background: none;
+  cursor: zoom-in;
+}
 .image img {
   width: 100%;
   height: 100%;