feat(hub-client): forward locale to FetchModuleDocs

Hub now accepts a locale field on FetchModuleDocsRequest so
README.<locale>.md (e.g. README.de.md) gets tried before the
generic README.md. SDK passes it via an optional named param;
empty string keeps the previous behaviour.

Signed-off-by: flemming-it <stefan.a.flemming@googlemail.com>

lib/src/hub_client.dart

@@ -240,8 +240,13 @@ class HubClient {
   /// when set, so Studio doesn't have to handle credentials.
   /// Errors come back inside [FetchModuleDocsResponse.errorKind]
   /// (not as exceptions) so the UI can render fallbacks.
-  Future<FetchModuleDocsResponse> fetchModuleDocs(String name) {
-    return _admin.fetchModuleDocs(pb.FetchModuleDocsRequest(name: name));
+  Future<FetchModuleDocsResponse> fetchModuleDocs(
+    String name, {
+    String locale = '',
+  }) {
+    return _admin.fetchModuleDocs(
+      pb.FetchModuleDocsRequest(name: name, locale: locale),
+    );
   }
 
   /// List every configured MCP server with the last-discovery