test: the user model and session refresh carry time_zone (milestone 490)

Run 8736: test_user_model_fields listed the columns without time_zone, and
the session-refresh fixture's users had no time_zone attribute. The refresh
test now also asserts a zone set on the Account page reaches the session.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

tests/test_models.py

@@ -5,7 +5,7 @@ def test_user_model_fields():
     """User model has all required fields."""
     cols = {c.key for c in User.__table__.columns}
     assert cols == {"id", "username", "email", "password_hash", "role", "created_at", "is_active",
-                    "auth_source", "external_id"}
+                    "auth_source", "external_id", "time_zone"}
 
 
 def test_user_role_enum():