fix(youtube): "this playlist no longer exists" only where the user picked that list

playlistNotFound was mapped to "gone" everywhere: exploring a channel without uploads (its
uploads list answers not found) and a list deleted mid bulk pull both said a playlist no
longer exists. The reason is now "gone" only on single-playlist routes; explore reads it
as an empty back-catalogue, and the bulk pull skips that list and syncs the rest.

backend/app/routes/playlists.py

@@ -372,7 +372,7 @@ def revert_youtube(
             raise not_found("playlist") from None
         except YouTubeError as exc:
             db.rollback()
-            raise youtube_refusal(exc) from exc
+            raise youtube_refusal(exc, playlist=True) from exc
 
 
 def _pushable(db: Session, user: User, playlist_id: int) -> Playlist:
@@ -398,7 +398,7 @@ def push_plan(
         with quota.attribute(user.id, quota.QuotaAction.PLAYLISTS_PUSH):
             plan = plan_merge(db, user, pl)
     except YouTubeError as exc:
-        raise youtube_refusal(exc) from exc
+        raise youtube_refusal(exc, playlist=True) from exc
     plan["remaining_today"] = quota.remaining_today(db)
     plan["affordable"] = plan["units_estimate"] <= plan["remaining_today"]
     return plan
@@ -439,7 +439,7 @@ def push(
             raise not_found("playlist") from None
         except YouTubeError as exc:
             db.rollback()
-            raise youtube_refusal(exc) from exc
+            raise youtube_refusal(exc, playlist=True) from exc
 
 
 @router.get("/{playlist_id}")
@@ -539,7 +539,7 @@ def delete_playlist(
                     with YouTubeClient(db, user) as yt:
                         yt.delete_playlist(pl.yt_playlist_id)
             except YouTubeError as exc:
-                raise youtube_refusal(exc) from exc
+                raise youtube_refusal(exc, playlist=True) from exc
         # The playlist first, as every item write: the cascade deletes the items before the list row.
         lock_playlists(db, pl.id)
         db.delete(pl)  # items cascade