The top nav was a mix of anchor links (#what, #features, #verify) and
site tabs (/plug-ins/, /extensions/). Sub-pages dropped the anchor-only
items, so the header visibly reshuffled between pages — clicking a tab
looked like a partial page break, not a navigation.
Top nav is now the same five items on every page: brand → Theseus.X,
Home / Plug-ins / Extensions / sirius.x / Get Theseus. Section anchors
moved to a fixed left sidebar (position: fixed, sits outside the
centered content column, hidden below 1180-1200px). IntersectionObserver
highlights the current section in acid green as the reader scrolls.
Sub-pages get their own left sidebar for the sections they actually
contain (Plug-ins: 3; Extensions: 6), so the pattern is consistent
across the site instead of home-only.
Brand text bumped to capital T + capital X.