Add CHANGELOG.md and SECURITY.md files

- Add standard Keep-a-Changelog style `CHANGELOG.md`.
- Add standard GitHub `SECURITY.md` policy.

Co-authored-by: Maatify <130119162+Maatify@users.noreply.github.com>

Author: google-labs-jules[bot]

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]
+
+## [1.0.0] - Initial Release
+
+### Added
+- Initial extraction of the validation module into the standalone library `maatify/validation`
+- Schema-based validation system
+- Validation rules
+- Validation result DTO
+- Error code enums
+- Schema abstraction
+- Pagination and query validation helpers

SECURITY.md

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+# Security Policy
+
+## Supported Versions
+
+The latest stable version receives security updates.
+
+| Version | Supported |
+| ------- | --------- |
+| 1.x     | Yes       |
+
+## Reporting a Vulnerability
+
+Please do not report security vulnerabilities through public GitHub issues.
+
+Instead, please report them privately by emailing [security@maatify.dev](mailto:security@maatify.dev).
+
+You should receive a response within 48 hours. If for some reason you do not, please follow up via email to ensure we received your original message.