migrate GroupChatJoinDialog to count prop

Finishes the invite-preview cleanup flagged in review: GroupChatJoinDialog was
the fourth surface hand-padding the profiles array, and its
Array(memberCount - 1) lacked the zero guard the others had (RangeError if
memberCount is 0). Using the count prop removes that latent edge case.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

src/components/intents/GroupChatJoinDialog.tsx

@@ -315,10 +315,8 @@ function GroupChatJoinDialogContent({code}: {code?: string}) {
     <>
       <View style={[a.w_full, a.py_lg, a.align_center]}>
         <AvatarBubbles
-          profiles={[
+          profiles={[joinLinkPreview.owner]}
-            joinLinkPreview.owner,
+          count={joinLinkPreview.memberCount}
-            ...Array(joinLinkPreview.memberCount - 1).fill(undefined),
-          ]}
           self
           size={135}
         />