api/create: always propagate :cloud source for cloud models (#14822)

Otherwise, using `/save` would try to run the local model instead

cmd/cmd_test.go

@@ -1345,6 +1345,20 @@ func TestNewCreateRequest(t *testing.T) {
 				Model: "newmodel",
 			},
 		},
+		{
+			"explicit cloud model preserves source when parent lacks it",
+			"newmodel",
+			runOptions{
+				Model:       "qwen3.5:cloud",
+				ParentModel: "qwen3.5",
+				Messages:    []api.Message{},
+				WordWrap:    true,
+			},
+			&api.CreateRequest{
+				From:  "qwen3.5:cloud",
+				Model: "newmodel",
+			},
+		},
 		{
 			"parent model as filepath test",
 			"newmodel",