Add `doseWindows` (Json?) to MedicationSchedule: a nullable array of
`{ timeOfDay, start, end }` HH:mm triples naming an explicit on-time
range for a dose time (e.g. 07:00–09:00). A time with no entry keeps the
symmetric ±1h default; a NULL column leaves every slot on the default
derivation, so the migration is additive and changes no existing
behaviour. Migration 0137 adds the column with no backfill.
