List Schools For Segment Selector

Just enough to populate the segment selector: id, name, slug.

Selects three columns by name rather than loading the Organization model, on purpose. Gamma routinely runs a migration or two behind development, and an ORM load fails wholesale on a column the database has not got yet — which would empty the school dropdown and take the entire per-school filter with it. Three columns that have existed since the table did cannot do that.