fix: 2图相册按真实比例+缩放贴合,竖图不再被裁

- albumLayout: 2 图不再 clamp 比例,格子按图片真实比例,避免下限 0.55 把竖图
  当矮图导致裁顶;3+ 张马赛克仍 clamp 保持整齐
- AlbumBubble: 2 图改用 object-contain,整图缩放贴合框内,永不裁剪;高度上限
  不变,不占用过多空间

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/components/messageStream/bubbles/AlbumBubble.tsx

@@ -26,6 +26,12 @@ export function AlbumBubble({ post }: { post: Post }) {
   const ratios = useImageRatios(visible, sources);
   const layout = computeAlbumLayout(ratios);
 
+  // Two-image albums scale each image to fit its cell (object-contain) so a
+  // tall poster is never cropped — the cell already matches the image ratio, so
+  // there are no bars except on very wide screens where the height is capped.
+  // 3+ images keep object-cover to stay a tidy mosaic.
+  const imgFit = visible.length === 2 ? "object-contain" : "object-cover";
+
   return (
     <div className="flex flex-col">
       {/* aspect-ratio sets a definite box height; tiles are absolutely
@@ -67,7 +73,7 @@ export function AlbumBubble({ post }: { post: Post }) {
                   src={sources[i]}
                   fallbackSrc={[att.thumbUrl, att.url]}
                   loading="lazy"
-                  className="h-full w-full object-cover transition duration-300 group-hover:scale-[1.03]"
+                  className={`h-full w-full ${imgFit} transition duration-300 group-hover:scale-[1.03]`}
                 />
                 {isLastSlot ? (
                   <div className="absolute inset-0 flex flex-col items-center justify-center gap-0.5 bg-black/60 text-white backdrop-blur-[1px] transition group-hover:bg-black/50">