doc(changelog): add changelog

CHANGELOG.md

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+# Changelog
+
+All notable changes to this project will be documented in this file.
+
+## 1.7.0 - 2026-04-21
+
+Changes since 1.6.1:
+
+### Added
+
+- Added scenario file storage and run artifact support on the backend.
+- Added file management UI for scenarios and run details, including artifact lists.
+- Added snippet CRUD tools to the MCP server.
+
+### Changed
+
+- Added dynamic page titles based on the active client content.
+- Extended the scenarios list to show the latest run status and timestamp.
+
+### Fixed
+
+- Exposed file expiry metadata in scenario and run file responses.
+- Disabled expired download actions in the UI while keeping the action visible.