sidebar crashes when items have type but no href #21

navlink throws on href.startsWith("http") when href is undefined

the sidebar uses "type" in item to split docmeta from sidebaritem, but this breaks when docmeta items have a type field from schema extension (e.g. frontmatter type: "guide"), they fall into the sidebaritem branch which passes undefined href to navlink

fix should check for href presence instead of type presence in the sidebar rendering logic, same issue exists in mobilenav and folder

pr #19 masks this by falling back href to "#" in navlink, which creates silent dead links