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/i18n/locales/en/channel.json

@@ -16,5 +16,8 @@
   "tabVideos": "Videos",
   "tabAbout": "About",
   "loadMore": "Load more from YouTube",
-  "noDescription": "This channel has no description."
+  "noDescription": "This channel has no description.",
+  "block": "Block channel",
+  "unblock": "Unblock channel",
+  "blockedBadge": "Blocked"
 }

frontend/src/i18n/locales/en/channels.json

@@ -123,5 +123,9 @@
   },
   "confirmUnsubscribe": "Unsubscribe from \"{{name}}\" on YouTube? This changes your real YouTube account. To just remove it from your feed, hide it instead.",
   "confirmReset": "Re-fetch \"{{name}}\" from scratch? This re-runs its backfill (recent + full history) and spends some API quota.",
-  "searchPlaceholder": "Search channels…"
+  "searchPlaceholder": "Search channels…",
+  "blocked": {
+    "title": "Blocked channels",
+    "hint": "Their videos are hidden from your feed, Library, and live search."
+  }
 }

frontend/src/i18n/locales/en/config.json

@@ -96,6 +96,10 @@
     "explore_grace_days": {
       "label": "Explore — grace period (days)",
       "hint": "How long an explored-but-unsubscribed channel (and its ephemeral videos) is kept before the cleanup job removes it. Subscribing keeps it permanently."
+    },
+    "search_grace_days": {
+      "label": "Search results — grace period (days)",
+      "hint": "How long an un-kept live-search result video (nobody watched / saved / subscribed to) is kept before the discovery-cleanup job removes it."
     }
   },
   "save": "Save",

frontend/src/i18n/locales/en/feed.json

@@ -48,6 +48,11 @@
     "noResults": "No YouTube videos found.",
     "error": "YouTube search failed.",
     "loadMore": "Load more (uses quota)",
-    "loadMoreFree": "Load more"
+    "loadMoreFree": "Load more",
+    "show": "Show",
+    "ephemeralNote": "These results are temporary — they clear automatically unless you watch or save one.",
+    "clearNow": "Clear now",
+    "cleared_one": "Cleared {{count}} result",
+    "cleared_other": "Cleared {{count}} results"
   }
 }

frontend/src/i18n/locales/en/scheduler.json

@@ -92,5 +92,8 @@
     "shortsPendingHint": "Enriched videos still awaiting the Shorts probe.",
     "liveRefresh": "Live to refresh",
     "liveRefreshHint": "Live/upcoming videos (and just-ended streams without a duration yet) re-checked until they settle."
-  }
+  },
+  "purgeDiscovery": "Purge discovery",
+  "purgeDiscoveryHint": "Remove all un-kept discovery content now (search results nobody watched/saved, and explored-but-unsubscribed channels) — ignoring the grace period.",
+  "purgedDiscovery": "Removed {{count}} discovery items"
 }