feat(feed): saved views as a header popover + Personal Views modal + a view chip

Retire the standalone 'Saved views' sidebar panel. The saved-views feature now
lives in three lighter surfaces, coordinated by a new SavedViewsProvider (query +
CRUD + the active/sticky view + modal state):

- the filter panel's header ICON opens a quick-pick popover (apply a view, active
  one checked, plus 'Manage views…');
- the header TITLE ('Filters') opens a new Personal Views modal — a master/detail
  manager: left = the reorderable list + a save-current-filters input, right = the
  selected view's name, its captured filters (shown as the same chips the toolbar
  row uses), default toggle, apply, and delete;
- a SelectedViewChip leads the applied-filter row, naming the active view with a
  warn-coloured 'modified' dot once the live filters diverge from it; clicking it
  reopens the picker.

SidePanel/FilterRail gain optional iconExpanded + onTitleClick slots (feed-only,
hidden for the demo account); the collapsed tab keeps its plain pin behaviour.
SavedViewsWidget is deleted and dropped from the panel layout.

Verified live: icon popover lists HH + Manage; applying HH surfaces the chip and
switches scope; removing a filter lights the dirty dot; the title opens the
master/detail modal with the captured-filters summary. 374 vitest, tsc, eslint
(0 err).

frontend/src/lib/panelLayout.ts

@@ -16,7 +16,7 @@ export interface PanelLayout {
 // Unknown/stale ids are dropped and any missing (e.g. a group added in a later version) are
 // appended by normalizeLayout, so nothing silently disappears.
 const PANEL_ORDER: Record<PanelId, string[]> = {
-  feed: ["savedviews", "date", "channel", "tags", "language", "topic"],
+  feed: ["date", "channel", "tags", "language", "topic"],
   plex: [
     "playlists",
     "watch",