Release Notes 26.0.1

This patch release improves DDC scale-down compatibility with Doris 4.1.3, adds repository-owned release automation, and makes pull request license checks safe for external contributors.

## Features & Enhancements

- Add repository-owned release tools for environment checks, source packaging, signing and upload, vote email generation, and release completion, with automated workflow tests. #507

## Bug Fixes

- Fixed DDC FE and compute group scale-down with Doris 4.1.3 by tolerating extended `SHOW FRONTENDS` and `SHOW BACKENDS` results, executing node removals individually, and making graceful backend cleanup retry-safe. #510

## Improve & Reliability

- Run the license check in a low-privilege `pull_request` workflow and update checkout handling so fork pull requests can be scanned safely. #511

## Thanks

- [morningman](https://github.com/morningman)
- [Al-assad](https://github.com/Al-assad)

Start by reviewing the release automation and its automated workflow tests, then compare the listed DDC compatibility and license-check changes with the repository's release process. Done means the 26.0.1 release notes and associated release work are complete and accurately reflect the changes described here.

Written by the indexing model from the issue text.