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/formats.py

@@ -13,6 +13,7 @@ spec shape (all keys optional; defaults applied by `normalize`):
     vcodec         "h264" | "vp9" | "av1" | null (preference, best-effort)
     embed_subs     bool     embed_chapters bool     embed_thumbnail bool     sponsorblock bool
 """
+
 import hashlib
 import json
 
@@ -215,8 +216,6 @@ def build_ydl_opts(
     # jpg/png thumbnail directly and converts anything else to PNG (not the crashing mjpeg2jpeg-to-jpg
     # path), so it never needed the convertor and does not reintroduce the crash.
     if s["embed_thumbnail"]:
-        opts["postprocessors"].append(
-            {"key": "EmbedThumbnail", "already_have_thumbnail": True}
-        )
+        opts["postprocessors"].append({"key": "EmbedThumbnail", "already_have_thumbnail": True})
 
     return opts