feat(search): ephemeral results UX, count selector, channel blocklist (frontend)

- Live-search view: a results-count selector (20/40/60/100) replaces manual load-more (the free
  scrape source pages until that many are gathered); an 'these results are temporary' banner with
  a 'Clear now' button that discards them 'as if never added' (api.clearSearch) and returns to
  the feed.
- Channel blocklist: a Block/Unblock toggle + 'Blocked' badge on the channel page (blocked
  channels don't auto-explore and their videos are hidden), and a 'Blocked channels' section in
  the Channel manager with one-click unblock. ChannelDetail.blocked from the backend.
- Admin: a 'Purge discovery' button on the Scheduler page (immediate un-kept search/explore
  cleanup). EN/HU/DE throughout.

frontend/src/components/Scheduler.tsx

@@ -13,6 +13,7 @@ import {
   Pencil,
   Play,
   RadioTower,
+  Trash2,
   X,
 } from "lucide-react";
 import { api, type SchedulerJob, type SchedulerStatus } from "../lib/api";
@@ -354,6 +355,15 @@ export default function Scheduler() {
     mutationFn: (v: number) => api.updateMaintenanceBatch(v),
     onSuccess: () => qc.invalidateQueries({ queryKey: ["scheduler"] }),
   });
+  const purgeMut = useMutation({
+    mutationFn: () => api.purgeDiscovery(),
+    onSuccess: (res) => {
+      const removed =
+        (res.search_videos_deleted ?? 0) + (res.videos_deleted ?? 0) + (res.channels_deleted ?? 0);
+      notify({ level: "success", message: t("scheduler.purgedDiscovery", { count: removed }) });
+      qc.invalidateQueries({ queryKey: ["scheduler"] });
+    },
+  });
 
   if (q.isLoading && !data)
     return <div className="p-8 text-muted">{t("scheduler.loading")}</div>;
@@ -398,6 +408,16 @@ export default function Scheduler() {
             {t("scheduler.runAll")}
           </button>
         </Tooltip>
+        <Tooltip hint={t("scheduler.purgeDiscoveryHint")}>
+          <button
+            onClick={() => purgeMut.mutate()}
+            disabled={purgeMut.isPending}
+            className="glass-card glass-hover flex items-center gap-2 px-3 py-2 rounded-xl text-sm disabled:opacity-50 transition"
+          >
+            <Trash2 className="w-4 h-4" />
+            {t("scheduler.purgeDiscovery")}
+          </button>
+        </Tooltip>
         <Tooltip hint={t("scheduler.pauseHint")}>
           <button
             onClick={() => pauseResume.mutate(data.paused)}