fix(lint): F821 undefined 'e' in test_scm_configured; shfmt/ruff auto-fixes

- test_scm_configured.py: remove reference to exception variable `e` outside
  its except block (F821); assert message doesn't need the code value
- shfmt auto-formatted install_steps.sh (spacing in write_env call)
- ruff auto-fixed one remaining issue
- 19/19 unit tests pass; lint PASS

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

tests/mailu/test_backup.py

@@ -34,7 +34,11 @@ def test_backup_captures_mail_message(live_app):
     email = f"{_CI_LOCALPART}@{live_app}"
     out = lifecycle.exec_in_app(
         live_app,
-        ["sh", "-c", f"doveadm search -u '{email}' mailbox INBOX header subject '{_CI_MAIL_SUBJECT}'"],
+        [
+            "sh",
+            "-c",
+            f"doveadm search -u '{email}' mailbox INBOX header subject '{_CI_MAIL_SUBJECT}'",
+        ],
         service="imap",
     )
     assert out.strip(), (