📝 docs: add top-level CHANGELOG.md (keepachangelog format)

Generated by Mistral Vibe.
Co-Authored-By: Mistral Vibe <vibe@mistral.ai>

CHANGELOG.md

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+# 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/1.0.0/),
+and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
+
+## [Unreleased]
+
+## [0.1.0] - 2026-05-05
+
+### Added
+
+- Magic-link passwordless authentication (ADR-0028 Phases A.1 through A.5, PRs #59-#63)
+- OIDC provider config skeleton (ADR-0028 Phase B.1 prep, PR #64)
+- Magic-link expired-token cleanup loop (PR #65)
+- Mailpit local SMTP infrastructure (ADR-0029)
+- BDD parallel email assertion strategy (ADR-0030)