fix: remove forced 4/3 aspect ratio and dark background from image containers

Images now size naturally within max constraints instead of being
letterboxed into a 4/3 bg-surface-input container. Fixes dark bars
on GIFs and images whose aspect ratio doesn't match 4/3.

packages/web/src/components/chat/Message.tsx

@@ -346,14 +346,11 @@ export function Message({ message, isCompact, isFirstInGroup, previousMessageId
         ) : (
           <div className="flex flex-col gap-1">
             {isGifOnly ? (
-              <div
-                className="mt-1 max-w-[250px] rounded-lg overflow-hidden bg-surface-input"
-                style={{ aspectRatio: '4/3', maxHeight: 250 }}
-              >
+              <div className="mt-1 max-w-[250px]">
                 <img
                   src={message.content!.trim()}
                   alt="GIF"
-                  className="w-full h-full object-contain rounded-lg"
+                  className="max-w-full max-h-[250px] rounded-lg"
                   loading="lazy"
                 />
               </div>