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_download_ref_count.py

@@ -9,6 +9,7 @@ conversion is provably behaviour-equivalent (concurrency itself can't be exercis
 
 DB lane (`db` fixture) — skipped without Postgres.
 """
+
 from sqlalchemy import select, text
 
 from app.downloads import service
@@ -31,8 +32,12 @@ def _ref_count(db, asset_id) -> int | None:
 
 def _holding_asset(db, *, status="ready", ref_count=1, rel_path=None) -> MediaAsset:
     asset = MediaAsset(
-        source_kind="url", source_ref=f"r{ref_count}-{status}", format_sig="sig",
-        status=status, ref_count=ref_count, rel_path=rel_path,
+        source_kind="url",
+        source_ref=f"r{ref_count}-{status}",
+        format_sig="sig",
+        status=status,
+        ref_count=ref_count,
+        rel_path=rel_path,
     )
     db.add(asset)
     db.flush()
@@ -41,8 +46,13 @@ def _holding_asset(db, *, status="ready", ref_count=1, rel_path=None) -> MediaAs
 
 def _job(db, user_id, asset_id, status="done") -> DownloadJob:
     j = DownloadJob(
-        user_id=user_id, asset_id=asset_id, source_kind="url", source_ref="r",
-        status=status, queue_pos=1, profile_snapshot={},
+        user_id=user_id,
+        asset_id=asset_id,
+        source_kind="url",
+        source_ref="r",
+        status=status,
+        queue_pos=1,
+        profile_snapshot={},
     )
     db.add(j)
     db.flush()
@@ -86,7 +96,9 @@ def test_release_is_a_noop_for_a_non_holding_job(db):
 
     service.release_asset(db, canceled)
     db.commit()
-    assert _ref_count(db, asset.id) == 1  # untouched — a canceled job already released while holding
+    assert (
+        _ref_count(db, asset.id) == 1
+    )  # untouched — a canceled job already released while holding
 
 
 def test_release_never_drives_ref_count_negative(db):