feat(views): saved-views UI — sidebar widget, apply/rename/default/reorder/share

A new "Saved views" filter-sidebar widget (SavedViewsWidget): save the
current filters under a name, apply one with a click (active-highlighted
when it matches), rename, delete (confirm), drag-reorder, share by link
(reuses shareUrl), and star one as the default. The default view's filters
are mirrored to localStorage so loadInitialFilters applies it synchronously
on load/F5 (an api/url share link still wins; no default → last-session
filters as before). Hidden for the demo account. EN/HU/DE.

frontend/src/i18n/locales/de/sidebar.json

@@ -31,6 +31,7 @@
   "shareCopied": "Ansichts-Link in die Zwischenablage kopiert",
   "shareFailed": "Link konnte nicht kopiert werden",
   "widget": {
+    "savedviews": "Gespeicherte Ansichten",
     "show": "Anzeigen",
     "sort": "Sortierung",
     "date": "Upload-Datum",