Initialize narratio Go module and CLI scaffold

internal/stage/stage.go

@@ -0,0 +1,21 @@
+package stage
+
+import (
+	"context"
+
+	"gitea.maximumdirect.net/eric/narratio/internal/app"
+	"gitea.maximumdirect.net/eric/narratio/internal/artifacts"
+	"gitea.maximumdirect.net/eric/narratio/internal/manifest"
+)
+
+// Stage is the pipeline unit contract.
+type Stage interface {
+	Name() string
+	Run(ctx context.Context, env *app.Env, m *manifest.Manifest) (*Result, error)
+}
+
+// Result is the declared output of a stage execution.
+type Result struct {
+	Outputs  []artifacts.Ref
+	Metadata map[string]any
+}