feat(sdk): add Generator interface and Registry

Defines the common interface for SDK generators with:
- Generate(), Available(), Install() methods
- Registry for managing multiple generators

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

pkg/sdk/generators/generator.go

@@ -0,0 +1,67 @@
+// Package generators provides SDK code generators for different languages.
+package generators
+
+import (
+	"context"
+)
+
+// Options holds common generation options.
+type Options struct {
+	// SpecPath is the path to the OpenAPI spec file.
+	SpecPath string
+	// OutputDir is where to write the generated SDK.
+	OutputDir string
+	// PackageName is the package/module name.
+	PackageName string
+	// Version is the SDK version.
+	Version string
+}
+
+// Generator defines the interface for SDK generators.
+type Generator interface {
+	// Language returns the generator's target language identifier.
+	Language() string
+
+	// Generate creates SDK from OpenAPI spec.
+	Generate(ctx context.Context, opts Options) error
+
+	// Available checks if generator dependencies are installed.
+	Available() bool
+
+	// Install returns instructions for installing the generator.
+	Install() string
+}
+
+// Registry holds available generators.
+type Registry struct {
+	generators map[string]Generator
+}
+
+// NewRegistry creates a registry with all available generators.
+func NewRegistry() *Registry {
+	r := &Registry{
+		generators: make(map[string]Generator),
+	}
+	// Generators will be registered in subsequent tasks
+	return r
+}
+
+// Get returns a generator by language.
+func (r *Registry) Get(lang string) (Generator, bool) {
+	g, ok := r.generators[lang]
+	return g, ok
+}
+
+// Register adds a generator to the registry.
+func (r *Registry) Register(g Generator) {
+	r.generators[g.Language()] = g
+}
+
+// Languages returns all registered language identifiers.
+func (r *Registry) Languages() []string {
+	langs := make([]string, 0, len(r.generators))
+	for lang := range r.generators {
+		langs = append(langs, lang)
+	}
+	return langs
+}