Add a CHANGELOG and a release note process

[sshdopey]

Context

There is no CHANGELOG, so contributors and users cannot see what changed between states of the app.

Scope

• Add a CHANGELOG and a short note on how entries are added.

Acceptance criteria

• A CHANGELOG exists with a documented update process.

Pointers

new CHANGELOG.md, CONTRIBUTING.md.

[bfernando]

@bfernando has applied to work on this issue as part of the Stellar Wave Program's 6th wave.

I'd like to work on this because it looks like a focused low-scope issue that can be handled without drifting beyond the request.

My relevant experience is in TypeScript/JavaScript, React/front-end fixes, API integrations, automation, and careful AI-assisted debugging with manual review.

For this issue, the relevant fit I see is: docs.

I will keep the docs change narrow and verify the links/content against the existing project structure.

I will stay within the issue scope, document exactly what I changed, link the PR back to the issue for Wave tracking, and include the validation I ran so the maintainer can review it quickly.

ℹ️ Repo Maintainers: To accept this application, review their application or assign @bfernando to this issue.