Convert update-release-branch.py to TypeScript

[mbg]

Converts the update-release-branch.py script to TypeScript following the same approach we have used to convert other legacy, Python scripts to TypeScript. The existing update-release-branch.py script had no tests. I have added some here, but adding full test coverage for this part of the automation requires a lot more work and refactoring of the new script. To keep it somewhat reviewable, the TypeScript version is kept similar to the Python one.

Risk assessment

For internal use only. Please select the risk level of this change:

• High risk: Changes are not fully under feature flags, have limited visibility and/or cannot be tested outside of production.

Which use cases does this change impact?

Environments:

• Testing/None - This change does not impact any CodeQL workflows in production.

How did/will you validate this change?

• Unit tests - I am depending on unit test coverage (i.e. tests in .test.ts files).
• None - I am not validating these changes.

If something goes wrong after this change is released, what are the mitigation and rollback strategies?

• Development/testing only - This change cannot cause any failures in production.

How will you know if something goes wrong after this change is released?

• Other - Please provide details.

Are there any special considerations for merging or releasing this change?

• No special considerations - This change can be merged at any time.

Merge / deployment checklist

• Confirm this change is backwards compatible with existing workflows.
• Consider adding a changelog entry for this change.
• Confirm the readme and docs have been updated if necessary.

[Copilot]

Pull request overview

Ports release-branch preparation and backport automation from Python to TypeScript.

Changes:

• Adds TypeScript release, changelog, API, and dry-run logic.
• Updates release workflows and dependency installation.
• Adds shared paths and editor skill settings.

Show a summary per file

File	Description
pr-checks/update-release-branch.ts	Implements release branch preparation and PR creation.
pr-checks/changelog.ts	Implements changelog transformations.
pr-checks/config.ts	Adds shared paths and dry-run options.
.github/workflows/update-release-branch.yml	Invokes the TypeScript script.
.github/actions/release-initialise/action.yml	Installs JavaScript dependencies.
.github/actions/release-branches/action.yml	Removes redundant dependency installation.
.vscode/settings.json	Adds agent skill locations.

Review details

• Files reviewed: 7/7 changed files
• Comments generated: 9
• Review effort level: Medium

[Copilot]

Review details

• Files reviewed: 9/9 changed files
• Comments generated: 3
• Review effort level: Medium

[henrymercer]

This has now been tested on a test repo, so let's try it out.