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/catalog/models.py

@@ -17,7 +17,6 @@ from sqlalchemy import (
     String,
     Text,
     UniqueConstraint,
-    and_,
     case,
     func,
     literal_column,
@@ -125,7 +124,7 @@ LIVE_OR_UPCOMING = ("live", "upcoming")
 # the stream has run (measured on prod, 2026-11-06: 122,962,914 s), and one such video made a Watch
 # later total read 44,073 hours. YouTube caps an upload at 12 hours, so nothing real is lost. Such a
 # length is unknown wherever a length is used: the API sends none (`Video.length_seconds`), sums leave
-# it out (a playlist's counts it as `live_without_length`), and the duration filter, sort and Home budget never
+# it out (a playlist's counts it as `without_length`), and the duration filter, sort and Home budget never
 # match it. The raw `duration_seconds` stays for what it does prove — that the video is not a Short —
 # and for the jobs that ask whether YouTube has answered yet (test_video_length holds who reads it).
 LENGTH_MAX_S = 24 * 3600
@@ -239,15 +238,16 @@ class Video(Base, TimestampMixin):
         )
 
     @hybrid_property
-    def live_without_length(self) -> bool:
-        """A live video (on air, upcoming, a premiere or an archive) whose length is unknown: what a
-        total leaves out and names as "+N live"."""
-        return self.live_status != "none" and self.length_seconds is None
+    def without_length(self) -> bool:
+        """A video whose length is unknown — live, an archive past a day, or not fetched yet: what a
+        sum of lengths leaves out and names as "+N without length". Every such video, so the count
+        and the sum never disagree about what was left out."""
+        return self.length_seconds is None
 
-    @live_without_length.inplace.expression
+    @without_length.inplace.expression
     @classmethod
-    def _live_without_length_expression(cls) -> ColumnElement[bool]:
-        return and_(cls.live_status != "none", cls.length_seconds.is_(None))
+    def _without_length_expression(cls) -> ColumnElement[bool]:
+        return cls.length_seconds.is_(None)
 
     # Weighted full-text search document (DB-generated, never written by the app): title (A) >
     # creator keywords + search queries (B) > truncated description (C). ts_rank honours the