lint: ruff format + one auto-fix so the push self-test is green again

`scripts/lint.sh --fix` from the pinned lint devshell: 90 Python files
reformatted (ruff format, mechanical) and one C420 (dict comprehension →
dict.fromkeys) in tests/unit/test_f211_sso_skip.py. The push self-test had
been failing at the lint stage since build 1313 (2026-08-31) on exactly
these files; nothing else changed.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01FqkQq3CDmFWcQ7u1LzoyRz

tests/mailu/custom/test_mailbox.py

@@ -24,6 +24,6 @@ def test_create_mailbox_and_read_back(live_app):
 
     cfg = _mailu.config_export(live_app)
     emails = _mailu.user_emails(cfg)
-    assert (
-        email in emails
-    ), f"created mailbox {email} not present in mailu config-export users {emails}"
+    assert email in emails, (
+        f"created mailbox {email} not present in mailu config-export users {emails}"
+    )