docs: per-client High-level walker example using LazyBrowseNode

Add a "High-level walker" subsection under each client's "Browsing
lazily" section showing idiomatic use of LazyBrowseNode (browse +
expand, idempotency note, redeploy refresh pattern).

clients/go/README.md

@@ -143,6 +143,46 @@ for i, child := range reply.GetChildren() {
 }
 ```
 
+#### High-level walker
+
+For UI trees, the client provides a `LazyBrowseNode` walker that handles
+sibling pagination and the `child_has_children` hint for you:
+
+```go
+galaxy, err := mxgateway.DialGalaxy(ctx, mxgateway.Options{
+    Endpoint:  "localhost:5000",
+    APIKey:    os.Getenv("MXGATEWAY_API_KEY"),
+    Plaintext: true,
+})
+if err != nil {
+    log.Fatal(err)
+}
+defer galaxy.Close()
+
+roots, err := galaxy.Browse(ctx, nil)
+if err != nil {
+    log.Fatal(err)
+}
+for _, root := range roots {
+    if root.HasChildrenHint() {
+        if err := root.Expand(ctx); err != nil {
+            log.Fatal(err)
+        }
+    }
+    for _, child := range root.Children() {
+        kind := "leaf"
+        if child.HasChildrenHint() {
+            kind = "has children"
+        }
+        fmt.Printf("%s (%s)\n", child.Object().GetTagName(), kind)
+    }
+}
+```
+
+`Expand` is idempotent — calling it twice fires only one RPC,
+and is safe under concurrent callers. To refresh after a Galaxy redeploy, call
+`Browse` again from the root.
+
 ### Watching deploy events
 
 `WatchDeployEvents` opens a server-streaming subscription. The server emits a