Implement authentication phase with Cidaas OAuth2 integration

- Add authentication middleware to protect routes
- Create API endpoints for login, logout, registration, and user info
- Develop UI components for login and registration forms
- Integrate VeeValidate for form validation
- Update environment configuration for Cidaas settings
- Add i18n support for English and German languages
- Enhance Tailwind CSS for improved styling of auth components
- Document authentication flow and testing procedures

server/api/auth/logout.post.ts

@@ -0,0 +1,24 @@
+// server/api/auth/logout.post.ts
+
+/**
+ * POST /api/auth/logout
+ *
+ * End user session and clear session cookie
+ *
+ * Response:
+ * {
+ *   "success": true
+ * }
+ */
+
+export default defineEventHandler(async (event) => {
+  // Clear session (nuxt-auth-utils)
+  await clearUserSession(event)
+
+  // Optional: Revoke Cidaas tokens (Single Sign-Out)
+  // This would require storing refresh_token in session and calling Cidaas revoke endpoint
+
+  return {
+    success: true,
+  }
+})