docs(repo): add keep-a-changelog formatted CHANGELOG.md

[shadrach68]

• closes docs: Create CHANGELOG.md with Keep a Changelog format #213

Summary

Creates the root CHANGELOG.md file adhering to the Keep a Changelog standard. This backfills the [Unreleased] section with recent features, fixes, and updates from the monorepo, and establishes the baseline [1.0.0] release entry to document our foundational services.

Type of change

• feat
• fix
• docs
• chore
• test
• ci

Checklist — author

• I rebased onto origin/main and resolved conflicts.
• I ran the quality gates locally: npm run lint, npm run build, npm test.
• Title follows Conventional Commits and references the issue (see above).
• No new TypeScript errors or lint warnings introduced.
• I updated documentation if the change affects public behavior.

[Xhristin3]

Appreciate the work on this! Keep a Changelog is a great standard and the backfill looks thorough. Merging.