fix: feedback round 2 — language, subscriptions, feed scope, UX

- Language detection: classify one cleaned+concatenated blob (strip emoji,
  @mentions, #tags, numbers, punctuation); fixes caps/emoji-heavy channels
  (e.g. Nessaj -> Hungarian, no more bogus Chinese/Korean)
- Feed now joins the user's subscriptions, so unsubscribing on YouTube removes a
  channel from the feed; periodic subscription re-sync job picks up changes
- Watched/Saved/Hidden views ignore the Shorts/live default-hiding so the full
  set is visible (fixes hidden videos missing from the Hidden view)
- Persist feed filters + search across reloads (localStorage)
- 3D polish: cards lift with shadow on hover; chips/buttons get depth and a
  press effect; undo toast lasts longer

backend/app/sync/runner.py

@@ -10,6 +10,7 @@ from sqlalchemy.orm import Session
 from app import quota
 from app.config import settings
 from app.models import Channel, OAuthToken, User
+from app.sync.subscriptions import import_subscriptions
 from app.sync.videos import (
     backfill_channel_deep,
     backfill_channel_recent,
@@ -65,6 +66,26 @@ def run_shorts(db: Session) -> dict:
     return run_shorts_classification(db)
 
 
+def run_subscription_resync(db: Session) -> dict:
+    """Re-import every user's subscriptions so unsubscribes and new subscriptions on
+    YouTube are reflected automatically."""
+    users = (
+        db.execute(
+            select(User)
+            .join(OAuthToken)
+            .where(OAuthToken.refresh_token_enc.is_not(None))
+        )
+        .scalars()
+        .all()
+    )
+    for user in users:
+        try:
+            import_subscriptions(db, user)
+        except Exception:
+            db.rollback()
+    return {"users": len(users)}
+
+
 def run_recent_backfill(
     db: Session, channels: list[Channel] | None = None, max_channels: int | None = None
 ) -> dict: