docs: implement automated CHANGELOG tracking

[rosspeili]

Problem Statement

Users and contributors currently have no way to see a high-level summary of changes between versions. Manually tracking every commit is tedious and prone to error.

Proposed Solution

1. Add a CHANGELOG.md file to the root of the repository.
2. Adopt a standard like Keep a Changelog.
3. (Optional) Investigate automated tools like conventional-changelog or GitHub Actions to generate entries from specially formatted commit messages.

Alternatives Considered

None. A clear changelog is essential for open-source project transparency.

Priority

Medium 🟡

Additional Context

This is a good-first-issue that helps improve project communication and versioning clarity.