Migrate to ESM and upgrade dependencies (#752)

* Migrate to ESM and upgrade dependencies

* Address review: use type-only import for QualityOptions

* update version to 6.0.0 in package.json and package-lock.json

* Add ESM migration note to README for V6

* Update test imports for ESM and clean up devDependencies (ts-node, @types/jest)

* Pin @types/node to 24.x and refine tsconfig/README wording

README.md

@@ -15,6 +15,10 @@ documentation:
 [Software installed on github hosted runners](https://docs.github.com/en/actions/using-github-hosted-runners/about-github-hosted-runners/about-github-hosted-runners#supported-software)
 for .NET SDK versions that are currently available.
 
+## What's new in V6
+
+- Migrated action internals to ESM for compatibility with latest `@actions/*` packages. No changes to action inputs, outputs, or behavior.
+
 ## Breaking changes in V5
 
 - Upgraded action from node20 to node24
@@ -410,4 +414,4 @@ The scripts and documentation in this project are released under the [MIT Licens
 
 ## Contributions
 
-Contributions are welcome! See [Contributor's Guide](docs/contributors.md)
+Contributions are welcome! See [Contributor's Guide](docs/contributors.md)