fix: remove .catch() from Supabase channel.subscribe() calls

RealtimeChannel.subscribe() returns the channel object, not a Promise.
Calling .catch() on it throws at runtime.

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

client/pages/Activity.tsx

@@ -1042,7 +1042,7 @@ function PollsTab({ userId, username }: { userId?: string; username?: string })
       },
     );
 
-    channel.subscribe().catch(() => {});
+    channel.subscribe();
     return () => {
       supabase.removeChannel(channel);
     };
@@ -2657,7 +2657,7 @@ function ChatTab({
       },
     );
 
-    channel.subscribe().catch(() => {});
+    channel.subscribe();
 
     return () => {
       clearInterval(interval);