feat: add authentication and user management with Authentik integration

- Add PostgreSQL database with async SQLAlchemy
- Add Alembic migrations for schema management
- Add User, Role, UserPreferences, ApiKey models
- Add auth endpoints: /auth/me, /auth/users, /auth/users/sync-from-authentik
- Add token validation via Authentik userinfo endpoint
- Add bulk user sync from Authentik admin API
- Add database health check to diagnostics

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

CHANGELOG.md

@@ -5,6 +5,26 @@ All notable changes to this project will be documented in this file.
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.1.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
+## [1.4.0] - 2026-01-01
+
+### Added
+
+- **Authentication & User Management** - Authentik integration for user synchronization
+  - `GET /auth/me` - Get current authenticated user info
+  - `GET /auth/users` - List all users with search and pagination
+  - `POST /auth/users/sync-from-authentik` - Bulk sync users from Authentik admin API
+- PostgreSQL database integration with async SQLAlchemy
+- Alembic database migrations for schema management
+- Database models: User, Role, UserPreferences, ApiKey
+- Token validation via Authentik userinfo endpoint
+- Role synchronization from Authentik groups
+- Health check now includes database connectivity status
+
+### Changed
+
+- Authentik configuration now uses username/password for admin API access
+- Health endpoint includes database status in diagnostics
+
 ## [1.3.1] - 2025-12-31
 
 ### Changed