Initialize narratio Go module and CLI scaffold

internal/manifest/manifest.go

@@ -0,0 +1,18 @@
+package manifest
+
+import "time"
+
+// StageState tracks status and metadata for one stage execution.
+type StageState struct {
+	Status    StageStatus
+	UpdatedAt time.Time
+	Error     string
+}
+
+// Manifest is the durable state record for a session run.
+type Manifest struct {
+	SessionID string
+	CreatedAt time.Time
+	UpdatedAt time.Time
+	Stages    map[string]StageState
+}