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/python/README.md

@@ -157,6 +157,30 @@ for child, has_children in zip(reply.children, reply.child_has_children):
     print(child.tag_name, "expand=" + str(has_children))
 ```
 
+#### High-level walker
+
+For UI trees, the client provides a `LazyBrowseNode` walker that handles
+sibling pagination and the `child_has_children` hint for you:
+
+```python
+async with await GalaxyRepositoryClient.connect(
+    endpoint="localhost:5000",
+    api_key="<gateway-api-key>",
+    plaintext=True,
+) as galaxy:
+    roots = await galaxy.browse()
+    for root in roots:
+        if root.has_children_hint:
+            await root.expand()
+        for child in root.children:
+            kind = "has children" if child.has_children_hint else "leaf"
+            print(f"{child.object.tag_name} ({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
 
 `GalaxyRepositoryClient.watch_deploy_events` opens a server-streaming