docs: Add CHANGELOG.md for v0.2.0 (#32)

* docs: add CHANGELOG.md documenting v0.2.0 release notes

Provide a Keep a Changelog file so consumers and contributors can
track notable changes for the 0.2.0 release and future work under
[Unreleased]. Closes #21 (LIM-139).

* docs: blank lines after CHANGELOG category headings (MD022)

Satisfy markdownlint blanks-around-headings after Added/Changed/Removed.

Author: rmems

CHANGELOG.md

@@ -0,0 +1,33 @@
+# Changelog
+
+All notable changes to this project will be documented in this file.
+
+The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.1.0/),
+and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
+
+## [Unreleased]
+
+## [0.2.0] - 2026-07-16
+
+### Added
+
+- GitHub Actions CI workflow (fmt, clippy, build, test)
+- Codecov coverage reporting (cargo-llvm-cov) and badge
+- Qodana static analysis CI
+- Dual MIT/Apache-2.0 license files and SPDX headers on Rust sources
+- `docs/BOUNDARY_MATRIX.md` documenting crate ownership boundaries
+- `examples/generic_environment.rs` domain-agnostic example
+- Local `ModulatorVector` type replacing sibling neuromod dependency (PR #29)
+- SimpleCritic acetylcholine derived from `Environment::surprise` (PR #30)
+
+### Changed
+
+- Rust edition 2021 → 2024
+- Declared MSRV `rust-version = "1.85"`
+- Critic output field `cortisol` → `norepinephrine`; wire `Environment::volatility()` → serotonin
+
+### Removed
+
+- Legacy mining/Qubic/Dynex documentation references
+- Unused `serde` dependency
+- Tracked CI log artifacts from the repository