docs: add CHANGELOG.md

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]
+
+### Added
+- Comprehensive `.gitignore` configuration for Python, Node, and OS-specific files.
+- `.editorconfig` for consistent editor settings across development environments.
+- `SECURITY.md` detailing the vulnerability reporting process.
+- `CONTRIBUTING.md` guide.
+- MIT License.
+- File type validation for backend upload endpoints.
+
+## [2.0.0] - 2024-03-15
+
+### Added
+- Complete rewrite to a local-first React + FastAPI architecture.
+- Advanced visualization engine using ECharts.
+- AI-powered chat and insight generation using DeepSeek or Anthropic.
+- Fully offline capability without LLM integration.
+- Dataset context management with SQLite.
+- Seamless CSV and Excel file ingestion with pandas profiling.
+- Automated data quality checks and smart cleaning suggestions.
+- Render-ready native deployment support.
+
+### Removed
+- Unused Dockerfiles and legacy stream processing scripts.