fix: address reader-UI feedback (shorts, search, tags, login, UX)

- Shorts: confirm via youtube.com/shorts/<id> probe (SOCS cookie bypasses the
  consent redirect) instead of a 60s heuristic; concurrent probing, shorts_probed
  flag, scheduled refinement (migration 0005)
- Search: match title + channel name only (descriptions caused noisy results)
- Faceted tag filtering: AND across categories (language AND topic narrows),
  OR within a category; any/all toggle applies to topics
- Language detection: majority vote over individual titles (fixes misdetections
  like multipoleguy -> English; drops bogus Polish/Romanian)
- Login: drop forced consent so returning sign-in is quick (select_account)
- Feed cards: clickable channel name (opens channel), persistent saved badge,
  undo toast on hide, Hidden view to restore; tag chips show counts in tooltip

backend/app/config.py

@@ -34,8 +34,11 @@ class Settings(BaseSettings):
     backfill_recent_max_videos: int = 100
     backfill_recent_max_days: int = 365
 
-    # Videos at or below this duration (seconds) are treated as Shorts.
-    shorts_max_seconds: int = 60
+    # Shorts are confirmed by probing youtube.com/shorts/<id>. Only videos at or below
+    # this duration (and not livestreams) are probed; longer videos are never Shorts.
+    shorts_probe_max_seconds: int = 180
+    shorts_probe_batch: int = 150
+    shorts_probe_interval_minutes: int = 2
     # videos.list accepts up to 50 ids per call.
     enrich_batch_size: int = 50