Returns the same full, detailed developer payload as GET /api/v2/clients/developers/{id}, but looked up by the developer's URL-friendly slug_name instead of its numeric id. Use this endpoint when you only have the slug — for example, when resolving SEO-friendly URLs, deep links shared externally, or cross-system references that carry the slug rather than the internal id. The response schema is identical to the id-based retrieve endpoint (RetrieveDeveloper). Returns 404 if no developer with the given slug_name exists.