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.

backend/tests/test_storage.py

@@ -1,5 +1,6 @@
 """On-disk layout helpers: name sanitation, the Plex/flat path shapes, and — most importantly —
 the safe_abs_path traversal guard that every file-serving endpoint depends on."""
+
 from datetime import date
 
 from app.downloads.storage import (
@@ -164,8 +165,9 @@ def test_sidecars_keep_the_full_basename_when_the_title_has_a_dot(tmp_path: Path
     media.write_text("x")
     thumb = tmp_path / "t.jpg"
     thumb.write_bytes(b"\xff\xd8\xff")
-    meta = MediaMeta(video_id="abc", title="Sonka Házilag. | Villám konyha", uploader="Chan",
-                     upload_date=None)
+    meta = MediaMeta(
+        video_id="abc", title="Sonka Házilag. | Villám konyha", uploader="Chan", upload_date=None
+    )
 
     assert write_sidecars(str(tmp_path), rel, meta, thumb) is True
     names = sorted(p.name for p in media.parent.iterdir())