fix(docs): use label-based API version mapping in docs-developers aztec-nr api page

Apply the equivalent of upstream fix 0e1c474 (PR #22617) to v4-next.
On next, the fix targets the v4.2.0 versioned snapshot; on v4-next that
snapshot does not exist yet, but docs-developers/docs/aztec-nr/api.mdx
— the source that will seed the next versioned cut — still carries the
stale name-based useApiVersion logic. Replacing it with the label-based
mapping prevents the same regression recurring when v4.2.0 developer
docs are cut from v4-next.

Author: AztecBot

docs/docs-developers/docs/aztec-nr/api.mdx

@@ -10,11 +10,13 @@ import { useActiveVersion } from "@docusaurus/plugin-content-docs/client";
 
 export const useApiVersion = () => {
   const version = useActiveVersion("developer");
-  const versionName = version?.name || "current";
-  // Map Docusaurus version to API docs folder
-  if (versionName === "current") return "next";
-  if (versionName.includes("rc") || versionName.includes("testnet")) return "testnet";
-  return versionName;
+  if (!version || version.name === "current") return "next";
+  // Map Docusaurus version to API docs folder using version label
+  // Labels are set explicitly in docusaurus.config.js (e.g., "Mainnet (...)")
+  const label = version.label || "";
+  if (label.startsWith("Alpha")) return "mainnet";
+  if (label.startsWith("Testnet")) return "testnet";
+  return version.name;
 };
 
 export const ModuleLink = ({ path, children }) => {