Create changetool script for validating change-notes

[mario-campos]

This PR introduces a distinct NPM package/script under scripts/changetool for the purpose of validating change-notes (and eventually, in a subsequent PR, merging change-notes into CHANGELOG.md).

Presently, this script has only one command, validate (executed as npm --prefix scripts/changetool start validate), which accepts path(s) to change-note files to be validated. Any flaws in the change-notes are described in the output, and the command will exit with 1.

$ npm --prefix scripts/changetool start validate package.json 

> changetool@1.0.0 start
> tsx index.ts validate package.json

package.json: invalid filename; must match pattern YYYY-MM-DD-id.md
package.json: invalid category; must be one of: breaking, feature, improvement, securityFix, fix, unship, deprecation, knownIssue, misc
package.json: invalid Markdown; content must be a single unordered list with hyphen bullets and no other Markdown elements

Risk assessment

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

• Low risk: Changes are fully under feature flags, or have been fully tested and validated in pre-production environments and are highly observable, or are documentation or test only.

Which use cases does this change impact?

Workflow types:

• N/A

Products:

• N/A

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).

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?

• N/A

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

Adds a standalone TypeScript CLI for validating change-note files.

Changes:

• Validates filenames, categories, and Markdown structure.
• Adds unit tests and package configuration.
• Integrates changetool testing and linting into CI.

Show a summary per file

File	Description
scripts/changetool/index.ts	Implements CLI dispatch and exit codes.
scripts/changetool/cli/validate.ts	Implements change-note validation.
scripts/changetool/cli/validate.test.ts	Tests validation behavior.
scripts/changetool/package.json	Defines scripts and dependencies.
scripts/changetool/package-lock.json	Locks package dependencies.
scripts/changetool/tsconfig.json	Configures TypeScript compilation.
eslint.config.mjs	Adds changetool lint configuration.
.github/workflows/pr-checks.yml	Adds a dedicated test job.

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• scripts/changetool/package-lock.json: Generated file

• Files reviewed: 7/8 changed files
• Comments generated: 7
• Review effort level: Balanced