problem-details-ktor-openapi

Teaches Ktor's OpenAPI generator to describe the problem responses a problem-details-ktor application actually produces: application/problem+json bodies, an RFC 9457 schema that admits extension members as siblings, and the status codes a problemDetails { } catalog answers.

Ktor infers an operation's responses from what its route handler calls. Problem documents come from StatusPages, which sits outside every route lambda, so inference can never see them and an otherwise complete document says nothing about failures. This module supplies them explicitly, through Ktor's own io.ktor.openapi model, so the result merges with whatever inference already found.