chore: configure 4.x maintenance branch

- Set semantic-release branch to 4.x
- Update CI triggers to 4.x branch
- Update README with maintenance notice

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

Author: brettstack

.github/workflows/release-on-push-to-mainline.yml

@@ -1,7 +1,7 @@
 name: CICD
 on:
   push:
-    branches: [mainline]
+    branches: [4.x]
   pull_request:
 env:
   HUSKY: 0
@@ -38,7 +38,7 @@ jobs:
         if: matrix.node-version == '20.x'
         run: npm audit --audit-level critical
   release:
-    if: github.event_name == 'push' && github.ref == 'refs/heads/mainline'
+    if: github.event_name == 'push' && github.ref == 'refs/heads/4.x'
     needs: test-lint-audit
     permissions:
       contents: write

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.
+> **This is the 4.x maintenance branch.** Only critical bug fixes. For new features, use v5: `npm install @codegenie/serverless-express`
 
 <h2 align="center">Serverless Express by</h1>
 <p align="center">

release.config.js

@@ -1,6 +1,6 @@
 module.exports = {
   branches: [
-    'mainline'
+    '4.x'
   ],
   plugins: [
     [