docs: add CHANGELOG.md and update README version to 1.6.0

- CHANGELOG.md: full history from 1.0.0 → 1.6.0 (Keep a Changelog format)
- README.md: bump version badge 1.5.0 → 1.6.0, add changelog summary table

README.md

@@ -10,7 +10,7 @@
                     A D M I N   B A C K E N D
 ```
 
-![Version](https://img.shields.io/badge/version-1.5.0-blue?style=for-the-badge)
+![Version](https://img.shields.io/badge/version-1.6.0-blue?style=for-the-badge)
 ![Django](https://img.shields.io/badge/Django-4.2-092E20?style=for-the-badge&logo=django&logoColor=white)
 ![DRF](https://img.shields.io/badge/DRF-3.15-red?style=for-the-badge)
 ![Python](https://img.shields.io/badge/Python-3.11-3776AB?style=for-the-badge&logo=python&logoColor=white)
@@ -145,6 +145,20 @@ eventify-django/
 
 ---
 
+## ✦ Changelog
+
+> Full history in [CHANGELOG.md](./CHANGELOG.md)
+
+| Version | Date | Summary |
+|---------|------|---------|
+| **1.6.0** | 2026-04-02 | Unique Eventify ID (`EVT-XXXXXXXX`) on User model, exposed across all APIs |
+| **1.5.0** | 2026-03-31 | `allowed_modules` field + `get_allowed_modules()` for RBAC |
+| **1.4.0** | 2026-03-24 | Partner portal login/logout/me APIs |
+| **1.3.0** | 2026-03-14 | User `id` → `BigAutoField` |
+| **1.0.0** | 2026-03-01 | Initial release — Django + JWT + Admin API |
+
+---
+
 ## ✦ Build Phases
 
 | Phase | Module | Endpoints | Status |