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

middleware/auth.ts

@@ -0,0 +1,28 @@
+// middleware/auth.ts
+
+/**
+ * Authentication middleware
+ *
+ * Protects routes from unauthenticated access
+ *
+ * Usage in pages:
+ *
+ * definePageMeta({
+ *   middleware: 'auth'
+ * })
+ */
+
+export default defineNuxtRouteMiddleware(async (to, from) => {
+  const { loggedIn } = useUserSession()
+
+  // Not logged in - redirect to auth page
+  if (!loggedIn.value) {
+    // Store intended destination for post-login redirect
+    useCookie('redirect_after_login', {
+      maxAge: 600, // 10 minutes
+      path: '/',
+    }).value = to.fullPath
+
+    return navigateTo('/auth')
+  }
+})