docs: added changelog

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/),
+and this project adheres to [Semantic Versioning](https://semver.org/).
+
+## [1.1.2] - 2026-03-02
+
+### Changed
+- Refined sample datasets to better demonstrate JSON tree navigation and edge cases.
+
+### Removed
+- Removed the integrated Changelog page from the system UI.
+
+## [1.1.1] - 2026-02-24
+
+### Added
+- Added syntax highlighting for JSONPath expressions to improve visual readability.
+
+## [1.1.0] - 2026-02-24
+
+### Added
+- Implemented sortable table views for JSON arrays with CSV export functionality.
+- Introduced a dedicated tool layout featuring a categorised sidebar menu for efficient switching.
+- Added one-click functionality to copy JSONPath-selected data as raw JSON.
+- Categorised tools into "JSON Processing" (Viewer, Grid) and "Daily Tools" (BMI Calculator).
+
+## [1.0.0] - 2026-01-19
+
+### Added
+- Initial release.
+- Full-featured JSON viewer with JSONPath query support and CSV export.
+- BMI calculator with category guidance and health advice.
+- Internationalisation support for British English and Simplified Chinese.