Retain coverage limits in legacy task summaries

Why: Older clients must see the same coverage limits as structured task cards.

Evidence: Core suite and composition checks follow this projection update.

Impact: Projects optional limitations into existing list nodes.

Refs: fast-slow-u2-u3 Task 6

task_snapshot.go

@@ -251,6 +251,9 @@ func (s TaskSnapshot) SummaryBody() []UINode {
 	if s.Coverage != "" {
 		body = append(body, UINode{Type: UIKV, KV: [][2]string{{"提供范围", s.Coverage}}})
 	}
+	if len(s.Limitations) > 0 {
+		body = append(body, UINode{Type: UIList, Title: "范围与限制", Items: s.Limitations})
+	}
 	for _, r := range s.ResultRefs {
 		if r.ArtifactID != "" && r.Availability == "available" {
 			body = append(body, UINode{Type: UIDocRef, DocID: r.ArtifactID, Title: r.Name})