Initialize narratio Go module and CLI scaffold

internal/adapters/notify/sender.go

@@ -0,0 +1,15 @@
+// Package notify declares the adapter contract for run notifications.
+package notify
+
+import "context"
+
+// Sender is a placeholder adapter interface for notifications.
+type Sender interface {
+	Send(ctx context.Context, msg Message) error
+}
+
+// Message is a placeholder notification payload.
+type Message struct {
+	Subject string
+	Body    string
+}