disable font scaling on fixed-height chat invite cards

thread a hasFixedHeight flag through ChatInvite.Root and its context so
the card, join button, and profile badges disable font scaling when they
live in a fixed-height container, preventing text from overflowing.

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

src/components/Post/Embed/ChatInviteEmbed.tsx

@@ -23,7 +23,7 @@ export function ChatInviteEmbed({
   style?: StyleProp<ViewStyle>
 }) {
   return (
-    <ChatInvite.Root code={code}>
+    <ChatInvite.Root code={code} hasFixedHeight>
       <ChatInviteEmbedBody link={link} onOpen={onOpen} style={style} />
     </ChatInvite.Root>
   )