chore(release): prepare 1.2.3-beta.0 beta package

[BlackishGreen33]

Summary

• prepare 1.2.3-beta.0 release metadata on top of the latest upstream main
• keep upstream README structure intact and add the beta entry to CHANGELOG.md
• bump runtime/package versions to 1.2.3-beta.0

Testing

• npm run build
• npm test -- --runInBand

[Copilot]

Pull request overview

Prepares the 1.2.3-beta.0 prerelease by bumping the package/plugin version metadata and recording the beta release entry in the changelog.

Changes:

• Bump package version to 1.2.3-beta.0.
• Update plugin runtime/version metadata (createRunOncePlugin + header comments) to 1.2.3-beta.0.
• Add v1.2.3-beta.0 entry to CHANGELOG.md and adjust historical entries.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 2 comments.

File	Description
plugin/src/index.ts	Updates plugin version annotations and the createRunOncePlugin version to 1.2.3-beta.0.
package.json	Bumps npm package version to 1.2.3-beta.0.
app.plugin.js	Updates header @version comment to 1.2.3-beta.0.
CHANGELOG.md	Adds v1.2.3-beta.0 entry and updates formatting/metadata for older entries.

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