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/utils.py

@@ -1,4 +1,5 @@
 """Small cross-cutting helpers shared across modules (kept dependency-light on purpose)."""
+
 import re
 from datetime import date, datetime, timezone
 
@@ -10,6 +11,7 @@ def iso(dt: date | None) -> str | None:
     too (datetime is a subclass) — e.g. MediaAsset.upload_date is a plain `date`."""
     return dt.isoformat() if dt is not None else None
 
+
 # Single source of truth for "looks like an email" — used by every endpoint that accepts an
 # address (auth register/reset/demo, admin invites + demo whitelist, the setup wizard). Keep
 # the strictness in one place so routes don't drift between this and a looser "@"-in check.