feat(gif-mood): masonry wall mode with DnD + flex columns

- Wall mode: flex columns (no empty bottoms), all GIFs mixed
- DnD in wall: SortableContext on current user items only, others are fixed
- Own GIFs show drag handle, others show avatar badge
- Image min-h skeleton prevents 0-height layout slots while loading

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/components/gif-mood/GifMoodCard.tsx

@@ -26,6 +26,7 @@ export const GifMoodCard = memo(function GifMoodCard({
   const [itemVersion, setItemVersion] = useState(item);
   const [isPending, startTransition] = useTransition();
   const [imgError, setImgError] = useState(false);
+  const [imgLoaded, setImgLoaded] = useState(false);
   const [isFocused, setIsFocused] = useState(false);
   const textareaRef = useRef<HTMLTextAreaElement>(null);
 
@@ -78,7 +79,8 @@ export const GifMoodCard = memo(function GifMoodCard({
         <img
           src={item.gifUrl}
           alt="GIF"
-          className="w-full block"
+          className={`w-full block ${imgLoaded ? '' : 'min-h-[80px]'}`}
+          onLoad={() => setImgLoaded(true)}
           onError={() => setImgError(true)}
         />
       )}