Add CHANGELOG.md

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: peterkacerik

CHANGELOG.md

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+# Changelog
+
+All notable changes to this project will be documented in this file.
+
+This project adheres to [Semantic Versioning](https://semver.org/).
+
+## [0.1.1] - 2026-03-15
+
+### Added
+- MIT LICENSE file
+- CI test workflow (Python 3.9-3.13)
+- PyPI trusted publisher workflow
+
+### Fixed
+- Node.js 20 deprecation warning in GitHub Actions
+
+## [0.1.0] - 2026-03-15
+
+### Added
+- Initial release
+- `AISpendGuard` client with batched threaded transport
+- Provider helpers: `create_openai_event`, `create_anthropic_event`, `create_gemini_event`
+- Tag validation (required tags, forbidden keys, privacy guard)
+- Streaming response documentation