chat: prevent reflow from image loading

Sets a static height on inline images in chat to prevent loss of scroll
position.

Fixes #2883

pkg/interface/src/apps/chat/components/lib/message.js

@@ -87,8 +87,8 @@ export class Message extends Component {
             className="o-80-d"
             src={letter.url}
             style={{
-              width: '50%',
-              maxWidth: '250px'
+              height: 'min(250px, 20vh)',
+              maxWidth: '80vw'
             }}
           ></img>
         );