Method OrderBy<TKey>(Expression<Func<TProps, TKey>>)

✅ FIX ISSUE #4: Override OrderBy to preserve Tree context
Base OrderBy returns RedbQueryable and loses Tree context!
RETURNS: IOrderedTreeQueryable (inherits from IOrderedRedbQueryable + preserves Tree methods)

public override IOrderedRedbQueryable<TProps> OrderBy<TKey>(Expression<Func<TProps, TKey>> keySelector)