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

internal/render/model.go

@@ -0,0 +1,24 @@
+package render
+
+// Transcript is the render-normalized transcript model used by renderers.
+type Transcript struct {
+	Schema   string
+	Metadata Metadata
+	Segments []Segment
+}
+
+// Metadata is the render-relevant artifact metadata.
+type Metadata struct {
+	Application string
+	Version     string
+}
+
+// Segment is a normalized render segment.
+type Segment struct {
+	ID         int
+	Start      float64
+	End        float64
+	Speaker    string
+	Text       string
+	Categories []string
+}