chore: configure 4.x maintenance branch and update docs for v5 stable

- Add 4.x maintenance branch to semantic-release config
- Update README to reflect stable v5 release

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: brettstack

README.md

@@ -1,9 +1,5 @@
 
-> **v5.0.0 Beta Released!** Version 5.0.0 is now available in beta with Node.js 24 support, removal of deprecated APIs, and a fix for nested routes and custom domains. Install with: `npm install @codegenie/serverless-express@beta`
->
-> Upgrading should be seamless unless you relied on deprecated APIs. See [UPGRADE.md](UPGRADE.md#from-4x-to-5x) for details.
->
-> **Note:** Version 4.x is now in maintenance mode and will only receive critical bug fixes.
+> **v5.0.0 Released!** Includes Node.js 24 support and removal of deprecated APIs. See [UPGRADE.md](UPGRADE.md#from-4x-to-5x) for upgrade instructions from v4.
 
 <h2 align="center">Serverless Express by</h1>
 <p align="center">

release.config.js

@@ -1,6 +1,7 @@
 module.exports = {
   branches: [
     'mainline',
+    { name: '4.x', range: '4.x', channel: '4.x' },
     { name: 'beta', prerelease: true }
   ],
   plugins: [