docs(changelog): CHANGELOG.md from git history

[pentaxis93]

Summary

Create a CHANGELOG.md following Keep a Changelog format, backfilled from the git history. The conventional commit messages (feat:, fix:, security:, docs:) make this straightforward. A changelog proves the project is actively maintained and helps users understand what changed between versions.

Part of: #3

Scope

• CHANGELOG.md — create at project root, organized by version with Added/Changed/Fixed/Security sections, backfilled from the ~114 commits using conventional commit prefixes

Acceptance criteria

• CHANGELOG.md exists at project root
• Follows Keep a Changelog format with version headers and categorized sections (Added, Changed, Fixed, Security)
• Covers significant changes from git history — at minimum the most recent meaningful commits
• Uses the current version (0.1.0) as the release version heading
• Includes an [Unreleased] section at the top for future changes

Dependencies

None — Layer 0, no blockers.