This also corrects the sleep schedule schema to actually store the
`is_active` field as `boolean` (it was `numeric`, which is the same
underlying field type in SQLite, but produces a different struct field
in the sqlc-generated Go code).
Ref: #104305
Workers can be soft-deleted, which means that they stay in the database.
As such, foreign key constraints `ON DELETE CASCADE` do not trigger, and
thus their sleep schedule can still be active. This is now detected and
handled gracefully.
