add a cache-control header to metadata page

cmd/appview/serve.go

@@ -392,6 +392,9 @@ func serveRegistry(cmd *cobra.Command, args []string) error {
 
 		w.Header().Set("Content-Type", "application/json")
 		w.Header().Set("Access-Control-Allow-Origin", "*")
+		// Limit caching to allow scope changes to propagate quickly
+		// PDS servers cache client metadata, so short max-age helps with updates
+		w.Header().Set("Cache-Control", "public, max-age=300")
 		if err := json.NewEncoder(w).Encode(metadataMap); err != nil {
 			http.Error(w, "Failed to encode metadata", http.StatusInternalServerError)
 		}