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/alembic/versions/0014_demo_account.py

@@ -11,6 +11,7 @@ Adds the shared demo-account plumbing:
 The demo user row itself is created lazily on first demo login (works across all three DBs
 without a data migration), so this only adds the schema.
 """
+
 from typing import Sequence, Union
 
 import sqlalchemy as sa
@@ -47,9 +48,7 @@ def upgrade() -> None:
             nullable=False,
         ),
     )
-    op.create_index(
-        "ix_demo_whitelist_email", "demo_whitelist", ["email"], unique=True
-    )
+    op.create_index("ix_demo_whitelist_email", "demo_whitelist", ["email"], unique=True)
 
 
 def downgrade() -> None: