fix: use gif image URL instead of giphy page URL in messages

gif.url is the giphy.com page link, gif.images.fixed_height.url is
the actual media CDN URL. react-markdown was rendering a dead link
instead of an embedded image.

web/src/components/ChatArea.tsx

@@ -245,7 +245,7 @@ export function ChatArea() {
 
   const handleGifSelect = async (gif: Gif) => {
     if (!activeChannelId) return;
-    const content = `![${gif.title || "GIF"}](${gif.url})`;
+    const content = `![${gif.title || "GIF"}](${gif.images.fixed_height.url})`;
     try {
       await sendMessage(activeChannelId, content);
       setShowGifPicker(false);