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/app/downloads/jobdb.py

@@ -1,4 +1,5 @@
 """Short-lived-session DB helpers + staging paths shared by the worker parent and the child pipeline."""
+
 from pathlib import Path
 
 from sqlalchemy import text
@@ -10,6 +11,7 @@ from app.models import DownloadJob, MediaAsset
 
 # --- small DB helpers (short-lived sessions; the download itself holds no transaction) -------
 
+
 def _set_job(job_id: int, **fields) -> None:
     with SessionLocal() as db:
         job = db.get(DownloadJob, job_id)