SDK.Generate() and SDK.GenerateLanguage() now use the
generator registry to generate SDKs for configured languages.
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
Initial pkg/sdk setup with Config types for OpenAPI SDK generation.
Includes language selection, diff config, and publish config.
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>