fix(playlists): "+N without length" counts every video the sum left out

The label said "without length" but the count held only live videos, so
a video not fetched yet, or gone before it was, was left out of the sum
and named nowhere. The server's `Video.without_length` and the client's
`isWithoutLength` are now one rule (no length, whatever the live
status), and the field, the key and the helpers are named for what they
count. The comments that still quoted "+N live" say the current copy.

backend/app/reader/queries.py

@@ -147,15 +147,15 @@ def item_counts(db: Session, ids: list[int]) -> dict[int, int]:
 
 
 def durations(db: Session, ids: list[int]) -> dict[int, tuple[int, int]]:
-    """Each playlist's running time — the sum of its videos' known lengths — and how many live videos
-    it cannot hold (`Video.live_without_length`)."""
+    """Each playlist's running time — the sum of its videos' known lengths — and how many videos
+    it left out for having none (`Video.without_length`)."""
     return {
-        pid: (int(total or 0), int(live or 0))
-        for pid, total, live in db.execute(
+        pid: (int(total or 0), int(left_out or 0))
+        for pid, total, left_out in db.execute(
             select(
                 PlaylistItem.playlist_id,
                 func.coalesce(func.sum(Video.length_seconds), 0),
-                func.count().filter(Video.live_without_length),
+                func.count().filter(Video.without_length),
             )
             .join(Video, Video.id == PlaylistItem.video_id)
             .where(PlaylistItem.playlist_id.in_(ids))
@@ -197,14 +197,14 @@ def covers(db: Session, ids: list[int]) -> dict[int, str | None]:
 
 
 def playlist_totals(db: Session, playlist_id: int) -> tuple[int, int, int, str | None]:
-    """One playlist's item count, running time, live videos the running time cannot hold
-    (`Video.live_without_length`) and cover. An outer join, so an empty list still answers
+    """One playlist's item count, running time, the videos the running time left out for having no
+    length (`Video.without_length`) and cover. An outer join, so an empty list still answers
     (0, 0, 0, None)."""
-    count, total, live = db.execute(
+    count, total, left_out = db.execute(
         select(
             func.count(PlaylistItem.id),
             func.coalesce(func.sum(Video.length_seconds), 0),
-            func.count().filter(Video.live_without_length),
+            func.count().filter(Video.without_length),
         )
         .select_from(PlaylistItem)
         .outerjoin(Video, Video.id == PlaylistItem.video_id)
@@ -217,7 +217,7 @@ def playlist_totals(db: Session, playlist_id: int) -> tuple[int, int, int, str |
         .order_by(PlaylistItem.position)
         .limit(1)
     )
-    return count or 0, total or 0, live or 0, cover
+    return count or 0, total or 0, left_out or 0, cover
 
 
 def playlist_rows(db: Session, user: User, playlist_id: int) -> list: