Developer resources, research data, and three screening fixes

New: Developers — every API with its OpenAPI 3.1 document and Postman collection where published, authentication, the error model, and a first call to make. Specs, collections and code examples are MIT-licensed; research data is CC BY 4.0. New: Data Sources & Freshness — each product’s upstream source, how it is read, and the source’s own stated update schedule, quoted.