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/i18n/locales/en/views.json

@@ -12,5 +12,13 @@
   "deleteConfirm": "Delete the saved view “{{name}}”?",
   "reorder": "Drag to reorder",
   "actionFailed": "Couldn't update your saved views — please try again.",
-  "reorderFailed": "Couldn't save the new order — please try again."
+  "reorderFailed": "Couldn't save the new order — please try again.",
+  "saved": "Saved views",
+  "manage": "Manage views…",
+  "manageTitle": "Personal views",
+  "capturedFilters": "Captured filters",
+  "capturedNone": "No filters — matches every video.",
+  "default": "Default",
+  "selectPrompt": "Select a view to see and edit it.",
+  "modified": "Modified — the current filters differ from this saved view."
 }

frontend/src/i18n/locales/hu/views.json

@@ -12,5 +12,13 @@
   "deleteConfirm": "Törlöd a(z) „{{name}}” mentett nézetet?",
   "reorder": "Húzd az átrendezéshez",
   "actionFailed": "Nem sikerült frissíteni a mentett nézeteket — próbáld újra.",
-  "reorderFailed": "Nem sikerült menteni az új sorrendet — próbáld újra."
+  "reorderFailed": "Nem sikerült menteni az új sorrendet — próbáld újra.",
+  "saved": "Mentett nézetek",
+  "manage": "Nézetek kezelése…",
+  "manageTitle": "Személyes nézetek",
+  "capturedFilters": "Rögzített szűrők",
+  "capturedNone": "Nincs szűrő — minden videóra illeszkedik.",
+  "default": "Alapértelmezett",
+  "selectPrompt": "Válassz egy nézetet a megtekintéshez és szerkesztéshez.",
+  "modified": "Módosítva — a jelenlegi szűrők eltérnek a mentett nézettől."
 }