Implement artifact-level render command with Markdown output and update docs

internal/render/registry.go

@@ -0,0 +1,41 @@
+package render
+
+import "fmt"
+
+const FormatMarkdown = "markdown"
+
+// Options configures rendering behavior across formats.
+type Options struct {
+	Title             string
+	IncludeTimestamps bool
+	IncludeSegmentIDs bool
+	IncludeMetadata   bool
+}
+
+// Renderer turns a normalized render model into text output.
+type Renderer interface {
+	Render(transcript Transcript, opts Options) (string, error)
+}
+
+// Registry resolves renderers by public format name.
+type Registry struct {
+	renderers map[string]Renderer
+}
+
+// NewRegistry returns a renderer registry with built-in renderers.
+func NewRegistry() Registry {
+	return Registry{
+		renderers: map[string]Renderer{
+			FormatMarkdown: MarkdownRenderer{},
+		},
+	}
+}
+
+// Resolve resolves a renderer by format name.
+func (registry Registry) Resolve(format string) (Renderer, error) {
+	renderer, ok := registry.renderers[format]
+	if !ok {
+		return nil, fmt.Errorf("unsupported --format %q", format)
+	}
+	return renderer, nil
+}