ui: re-introduce adaptive download pill sizing for album tiles

- AttachmentDownloadPill: bring back the optional adaptive sizing
  branch (default off). When the host sets containerType: inline-size,
  the pill scales 22-30px with the tile width using a steeper
  18cqw curve, so two-image tiles already reach 30px while tiny
  thumbs in mixed layouts stay at 22px.
- AlbumBubble: opt every tile into adaptive sizing and add the query
  container so the cqw units resolve against each tile's width.
- Single-image and video bubbles continue to render the pill at a
  fixed 30px (no host opt-in needed).

src/components/messageStream/bubbles/AlbumBubble.tsx

@@ -51,6 +51,8 @@ export function AlbumBubble({ post }: { post: Post }) {
                 top: `${tile.top * 100}%`,
                 width: `calc(${tile.width * 100}% - ${ALBUM_GAP}px)`,
                 height: `calc(${tile.height * 100}% - ${ALBUM_GAP}px)`,
+                // Query container so the download pill scales with this tile.
+                containerType: "inline-size",
               }}
             >
               <button
@@ -76,7 +78,11 @@ export function AlbumBubble({ post }: { post: Post }) {
                 ) : null}
               </button>
               {!isLastSlot ? (
-                <AttachmentDownloadPill postId={post.id} attachment={att} />
+                <AttachmentDownloadPill
+                  postId={post.id}
+                  attachment={att}
+                  adaptive
+                />
               ) : null}
             </div>
           );