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/sync/subscriptions.py

@@ -1,4 +1,5 @@
 """Import the authenticated user's YouTube subscriptions and channel metadata."""
+
 import logging
 from datetime import datetime, timezone
 
@@ -57,9 +58,7 @@ def apply_channel_details(db: Session, items: list[dict]) -> None:
         channel.title = snippet.get("title") or channel.title
         channel.handle = snippet.get("customUrl")
         channel.description = normalize_description(snippet.get("description"))
-        channel.thumbnail_url = (
-            best_thumbnail(snippet.get("thumbnails")) or channel.thumbnail_url
-        )
+        channel.thumbnail_url = best_thumbnail(snippet.get("thumbnails")) or channel.thumbnail_url
         channel.default_language = snippet.get("defaultLanguage")
         channel.country = snippet.get("country")
         channel.uploads_playlist_id = content.get("relatedPlaylists", {}).get("uploads")
@@ -125,16 +124,15 @@ def import_subscriptions(db: Session, user: User) -> dict:
         # (see `should_prune`).
         removed = 0
         existing = (
-            db.execute(select(Subscription).where(Subscription.user_id == user.id))
-            .scalars()
-            .all()
+            db.execute(select(Subscription).where(Subscription.user_id == user.id)).scalars().all()
         )
         prune_skipped = not should_prune(len(fetched), len(existing))
         if prune_skipped:
             log.warning(
                 "Subscription import (user %s): YouTube returned 0 subscriptions while %d exist "
                 "locally — skipping the prune (treating it as a transient empty response)",
-                user.id, len(existing),
+                user.id,
+                len(existing),
             )
         else:
             for sub_row in existing: