SQLAlchemy 2.0 defaults to mapping Python enum *names* (OPEN, CLOSED)
to DB values, but MySQL stores lowercase *values* (open, closed).
This mismatch causes LookupError on read.
Adding values_callable=lambda x: [e.value for e in x] tells SQLAlchemy
to use the enum values for DB mapping.
Affected models: milestone, task, meeting, propose, support
