Memory Leak from Unremoved Event Listeners

1. window/document listeners not removed in useEffect cleanup
2. Supabase subscriptions not unsubscribed
3. setTimeout/setInterval not cleared
4. Observable subscriptions not unsubscribed
5. Event handlers recreated on every render

Clean up listeners in useEffect return:

useEffect(() => {
  const handleResize = () => setWidth(window.innerWidth);
  window.addEventListener('resize', handleResize);
  
  return () => {
    window.removeEventListener('resize', handleResize);
  };
}, []);

Always unsubscribe from Supabase and clean up timers:

useEffect(() => {
  const id = setTimeout(() => {}, 1000);
  return () => clearTimeout(id);
}, []);