feat(plex): S3 toolbar relocation — scope to header, sort above the cards

Move the two "what am I browsing" controls out of the filter sidebar to where
they're always in reach, matching the Feed's layout:

- Library scope (both/movie/show) → a compact SegmentedToggle in the header next
  to the search box (new PlexScopeToggle, reads the same provider state).
- Sort → a SortControl in the row above the cards (into the PageToolbar band,
  count on the left, sort on the right), like the Feed.

Sidebar cleanup: drop the `scope` and `sort` island cards; the panel badge now
counts only the filters still in the panel (expanded filters + watch-state);
remove the now-unused sort imports. panelLayout drops both from the default plex
order (stale saved-layout keys are auto-filtered, so existing layouts degrade
cleanly). usePlexActiveFilters no longer emits a sort chip — sort is an
always-visible control now, not a removable narrowing (same as the Feed).

FE-only, no backend/migration. typecheck + eslint clean; 171 vitest green;
self-E2E verified (header scope drives the grid, sort control reorders, sidebar
no longer shows the two cards, no sort chip).

frontend/src/lib/panelLayout.ts

@@ -18,10 +18,8 @@ export interface PanelLayout {
 const PANEL_ORDER: Record<PanelId, string[]> = {
   feed: ["savedviews", "date", "channel", "tags", "language", "topic"],
   plex: [
-    "scope",
     "playlists",
     "watch",
-    "sort",
     "people",
     "collection",
     "rating",