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
Milestone: open/freeze/undergoing/completed/closed (was open/pending/deferred/progressing/closed)
Task: open/pending/undergoing/completed/closed (was open/pending/progressing/closed)
- Add MilestoneStatusEnum to schemas with typed validation
- Add started_at field to Milestone model
- Update all router/CLI references from progressing->undergoing
- Add completed status handling in task transition logic
