style: apply ruff format across backend + scripts (line-length 100)

Mechanical, whole-tree `ruff format` pass — no behaviour change. Recorded in
.git-blame-ignore-revs (next commit) so git blame skips it.

scripts/e2e_seed.py

@@ -114,10 +114,7 @@ def main() -> None:
             if exclude:
                 conds.append(Video.id.not_in(exclude))
             return db.scalar(
-                select(Video)
-                .where(*conds)
-                .order_by(Video.published_at.desc())
-                .limit(1)
+                select(Video).where(*conds).order_by(Video.published_at.desc()).limit(1)
             )
 
         used: set[str] = set()
@@ -154,9 +151,7 @@ def main() -> None:
         # 4. One "saved" video (Watch-later membership drives the saved marker) from the last
         #    subscribed channel. Reset the built-in playlist's items each run.
         wl = db.scalar(
-            select(Playlist).where(
-                Playlist.user_id == user.id, Playlist.kind == "watch_later"
-            )
+            select(Playlist).where(Playlist.user_id == user.id, Playlist.kind == "watch_later")
         )
         if wl is None:
             wl = Playlist(user_id=user.id, name="Watch later", kind="watch_later")