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/components/Sidebar.tsx

@@ -39,6 +39,7 @@ import { notify } from "../lib/notifications";
 import { useDebounced } from "../lib/useDebounced";
 import { Switch } from "./ui/form";
 import TagManager from "./TagManager";
+import SavedViewsWidget from "./SavedViewsWidget";
 
 // Filter ids; display labels resolved at render time via t("sidebar.sort.<id>") etc.
 const SORT_IDS = [
@@ -118,12 +119,14 @@ export default function Sidebar({
   layout,
   setLayout,
   onFocusChannel,
+  isDemo = false,
 }: {
   filters: FeedFilters;
   setFilters: (f: FeedFilters) => void;
   layout: SidebarLayout;
   setLayout: (l: SidebarLayout) => void;
   onFocusChannel: (name: string) => void;
+  isDemo?: boolean;
 }) {
   const { t } = useTranslation();
   const tagsQuery = useQuery({ queryKey: ["tags"], queryFn: api.tags });
@@ -228,6 +231,9 @@ export default function Sidebar({
   }
 
   const available: Record<WidgetId, boolean> = {
+    // Saved views are personal state; hide the widget for the shared demo account (the API
+    // also rejects the writes via require_human).
+    savedviews: !isDemo,
     date: true,
     language: languages.length > 0,
     topic: topics.length > 0,
@@ -251,6 +257,8 @@ export default function Sidebar({
 
   function widgetBody(id: WidgetId): React.ReactNode {
     switch (id) {
+      case "savedviews":
+        return <SavedViewsWidget filters={filters} onApply={setFilters} />;
       case "date":
         return (
           <>