Orval: Import-time RCE via header-parameter default -> zod module-level template literal

Orval generates type-safe JavaScript clients in TypeScript from OpenAPI v3 and Swagger v2 specifications. Prior to 8.21.0, a ${...} expression or backtick in a header parameter default is emitted into a module-level template literal emitted by zod schema generation without safe encoding. This permits attacker-controlled JavaScript to be evaluated when the generated zod schema module is imported, resulting in code execution in the developer, CI, test, or application environment. The affected code is packages/zod/src/index.ts function formatDefaultValue. This issue is fixed in version 8.21.0.