The scope toggle used to sit at the top of the filter rail, which is buried when
the rail is collapsed/unpinned. Relocate it to the header, just right of the feed
search box — mirroring Plex's scope toggle placement — so the primary 'what am I
browsing' control is always visible.
New FeedScopeToggle adapter (SegmentedToggle over filters.scope, same as the Plex
one over its scope); rendered in Header on the feed page between the search box and
the sync chip. Removed the toggle from the Sidebar rail's now-unused `top` slot and
dropped the dead `top` prop from FilterRail. Same filters.scope field, so behaviour
is unchanged.
Verified live: the toggle sits beside the feed search and switches scope; the rail
no longer carries it.
