Currently the wiki skin is generating double , and tags, because it's stacking the SMF header on top of mediawiki's one.
Ideally it would use SMF's header, but intelligently inject mediawiki's required includes and title tag into it. The tag should also be mediawiki's, because it includes classes which could be helpful for fine-tuned styling.
Possible solution: when executing SMF's header template, strip out tags we don't want such as the
<title>, and then when generating mediawiki's header do so likewise for tags we don't want coming from it.