feat(filters): scope global feed filters in FeedFiltersProvider

Lift the feed's filter god-state (per-account persistence, the account-load
effect, share-link capture) out of App into a split-context provider mirroring
NavigationProvider. Sidebar/Header/NotificationsPanel read it via hooks instead
of prop-drilling; <Feed> keeps its filters prop since ChannelPage renders it with
its own channel-scoped state.

frontend/src/components/NotificationsPanel.tsx

@@ -2,7 +2,7 @@ import { useEffect, useSyncExternalStore } from "react";
 import { useTranslation } from "react-i18next";
 import { useMutation, useQueryClient } from "@tanstack/react-query";
 import { Activity, Bell, Check, CheckCheck, ExternalLink, Eye, RotateCcw, Search, Trash2, Tv, UserPlus, X } from "lucide-react";
-import { api, type AppNotification, type FeedFilters } from "../lib/api";
+import { api, type AppNotification } from "../lib/api";
 import { useLiveQuery } from "../lib/useLiveQuery";
 import { focusAccessRequestsTab } from "../lib/adminUsersTab";
 import {
@@ -23,6 +23,7 @@ import { channelYouTubeUrl, relativeFromMs, relativeTime } from "../lib/format";
 import { LEVEL_STYLE } from "./Toaster";
 import { PageToolbar } from "./PageShell";
 import { useNavigationActions } from "./NavigationProvider";
+import { useFeedFilters, useFeedFiltersActions } from "./FeedFiltersProvider";
 
 // The single notification center. "System" = durable, server-backed notifications (inbox
 // phase 1). "Activity" = the client-side transient events (action confirmations, errors, with
@@ -31,16 +32,14 @@ import { useNavigationActions } from "./NavigationProvider";
 const POLL_MS = 8000;
 
 export default function NotificationsPanel({
-  filters,
-  setFilters,
   onFocusChannel,
 }: {
-  filters: FeedFilters;
-  setFilters: (f: FeedFilters) => void;
   onFocusChannel: (name: string) => void;
 }) {
   const { t } = useTranslation();
   const { setPage } = useNavigationActions();
+  const filters = useFeedFilters();
+  const { setFilters } = useFeedFiltersActions();
   const qc = useQueryClient();
   const q = useLiveQuery<{ items: AppNotification[]; total: number }>(
     ["notifications"],