api: make _pager a helper

lib/PoorBooru/API/V0.pm

@@ -17,6 +17,10 @@ sub startup ($self)
 	$self->helper(schema => sub {
 		state $schema = PoorBooru::Schema->connect($config->{dsn})
 	});
+	$self->helper(pager => sub ($, $dbp) {
+		map +( $_ => $dbp->$_ ), qw(first_page previous_page
+		    current_page next_page last_page)
+	});
 
 	my $r = $self->routes;