feat(scheduler): live admin Scheduler dashboard + reusable poll hook (HU/EN/DE)

New admin Scheduler page (left-nav entry) with a live, self-refreshing view of
job activity, queued work and quota. Polling is factored into a reusable
useLiveQuery hook (pauses when the tab is unfocused) that the notification bell
and future yt-dlp job queue will reuse instead of re-implementing.

frontend/src/lib/api.ts

@@ -303,6 +303,39 @@ export interface ManagedChannel {
   backfill_done: boolean;
 }
 
+export interface SchedulerJob {
+  id: string;
+  interval_minutes: number;
+  next_run: string | null;
+  running: boolean;
+  status: "ok" | "error" | "skipped" | null;
+  last_started: string | null;
+  last_finished: string | null;
+  last_result: string | null;
+  last_error: string | null;
+}
+
+export interface SchedulerStatus {
+  running_here: boolean;
+  enabled: boolean;
+  paused: boolean;
+  jobs: SchedulerJob[];
+  queue: {
+    channels_recent_pending: number;
+    channels_deep_pending: number;
+    deep_eta_seconds: number;
+    videos_pending_enrich: number;
+    videos_pending_shorts: number;
+    videos_live_refresh: number;
+  };
+  quota: {
+    used_today: number;
+    remaining_today: number;
+    daily_budget: number;
+    backfill_reserve: number;
+  };
+}
+
 export interface Account {
   id: number;
   email: string;
@@ -400,6 +433,7 @@ export const api = {
   // --- quota usage ---
   myUsage: (): Promise<MyUsage> => req("/api/quota/my-usage"),
   adminQuota: (days = 30): Promise<AdminQuota> => req(`/api/quota/admin?days=${days}`),
+  schedulerStatus: (): Promise<SchedulerStatus> => req("/api/admin/scheduler"),
 
   // --- onboarding / admin ---
   requestAccess: (email: string): Promise<{ status: string }> =>

frontend/src/lib/urlState.ts

@@ -78,11 +78,15 @@ export function hasFilterParams(params: URLSearchParams): boolean {
   return KEYS.some((k) => params.has(k));
 }
 
-export type Page = "feed" | "channels" | "stats" | "playlists" | "settings";
+export type Page = "feed" | "channels" | "stats" | "playlists" | "settings" | "scheduler";
 
 export function readPage(): Page {
   const p = new URLSearchParams(window.location.search).get("page");
-  return p === "channels" || p === "stats" || p === "playlists" || p === "settings"
+  return p === "channels" ||
+    p === "stats" ||
+    p === "playlists" ||
+    p === "settings" ||
+    p === "scheduler"
     ? p
     : "feed";
 }

frontend/src/lib/useLiveQuery.ts

@@ -0,0 +1,22 @@
+import { useQuery, type QueryKey } from "@tanstack/react-query";
+
+// Reusable "live" polling query: a thin wrapper over react-query that refetches on an
+// interval and — by leaving refetchIntervalInBackground at its default false — pauses while
+// the tab is unfocused, so it doesn't poll a server nobody's watching. This is the shared
+// live-progress mechanism: the Scheduler dashboard uses it now; the notification bell and the
+// future yt-dlp job queue reuse it rather than each re-implementing polling.
+export function useLiveQuery<T>(
+  key: QueryKey,
+  queryFn: () => Promise<T>,
+  opts: { intervalMs?: number; enabled?: boolean } = {}
+) {
+  const { intervalMs = 4000, enabled = true } = opts;
+  return useQuery({
+    queryKey: key,
+    queryFn,
+    enabled,
+    refetchInterval: enabled ? intervalMs : false,
+    refetchIntervalInBackground: false,
+    staleTime: 0,
+  });
+}