docs: add CHANGELOG.md

CHANGELOG.md

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+# Changelog
+
+All notable changes to this project are 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). The CLI contract is versioned
+independently as `contract_version` (currently **1.1**) — integrators depend on that, not the package
+version; see [docs/reference/cli.md](docs/reference/cli.md).
+
+## [Unreleased]
+
+## [0.1.0] - 2026-07-08
+
+Initial public release.
+
+### Added
+
+- **Deterministic `ea-core` engine + `ea` CLI** behind a stable, versioned CLI contract
+  (`contract_version` 1.1). Identical inputs produce byte-identical output — no LLM, no network, no
+  wall-clock. Every mutation is dry-run by default and gated on a content-bound `--confirm` token.
+- **Command surface:** `init`, `validate`, `report`, `graph`, `scaffold`, `show`, `commit`,
+  `promote`, `migrate`, `method`, `manifest`, `project`, `pack`, `preset`, `type`, and `version`.
+- **Method packs as data** — artifact types, methods, relationships, and validation rules are
+  versioned YAML read at runtime; the constraint-kind vocabulary is closed and packs never carry
+  code. Adopting a methodology is configuration, not a code change.
+- **Adapter surfaces** — the `ea-claude` and `ea-antigravity` plugins hosting the `ea-architect`
+  and `ea-methodologist` skills. AI supplies only judgment on the surface; the core decides and
+  writes.
+- **Production method library** — three pack + archetype-preset pairs: `enterprise-architecture`,
+  `lean-ux`, and `open-agile-architecture`, fetchable into a local cache with `ea pack fetch`.
+- **Documentation** — principles, architecture, CLI / repository / packs / manifest / surfaces
+  reference, quickstart + tailoring guides, and binding decision records under `docs/`.
+
+[Unreleased]: https://github.com/adworzynski/ea-as-a-code/compare/v0.1.0...HEAD
+[0.1.0]: https://github.com/adworzynski/ea-as-a-code/releases/tag/v0.1.0