The Automations page reuses the music builder, whose .automations-builder-view is
height:100% so its trigger/action sidebar + canvas scroll independently. On music it
fills #automations-page (a .page at height:100%); on video it sat in a .video-subpage
with no height, so height:100% collapsed to content height and the sidebar grew
instead of scrolling (looked unformatted). #video-page-host is itself a .page, so
give just the automations subpage a definite height to resolve the chain. Scoped to
automations so every other video page keeps its natural document-flow scroll.
