Initialize narratio Go module and CLI scaffold

internal/artifacts/store.go

@@ -0,0 +1,19 @@
+package artifacts
+
+import "context"
+
+// Ref identifies a pipeline artifact and optional remote location.
+type Ref struct {
+	Kind      string
+	LocalPath string
+	RemoteKey string
+	Checksum  string
+}
+
+// Store is a placeholder artifact storage abstraction.
+type Store interface {
+	WriteLocal(ctx context.Context, ref Ref, data []byte) error
+	ReadLocal(ctx context.Context, ref Ref) ([]byte, error)
+	ExistsLocal(ctx context.Context, ref Ref) (bool, error)
+	Upload(ctx context.Context, ref Ref) (string, error)
+}