Add registration functionality and update authentication views

- Implemented a new method in AuthController to display the registration form with localized labels and session error handling.
- Updated the login view to include a link for account creation.
- Enhanced the registration view with a link to the login form.
- Removed the obsolete showRegisterPage view to streamline the codebase.

Controller/AuthController.php

@@ -30,6 +30,21 @@ class AuthController
         unset($_SESSION['auth_errors'], $_SESSION['auth_validData']);
     }
 
+    public function showRegistrationForm()
+    {
+        $this->view->setVars([
+            'labels' => [
+                "email" => "E-Mail-Adresse",
+                "password" => "Passwort",
+                "password_repeat" => "Passwort wiederholen",
+                "old_password" => "Altes Passwort"
+            ],
+            'errors' => $_SESSION['auth_errors'] ?? [],
+            'validData' => $_SESSION['auth_validData'] ?? []
+        ]);
+        unset($_SESSION['auth_errors'], $_SESSION['auth_validData']);
+    }
+
     public function login() {
         $email = $_POST['email'];
         $password = $_POST['password'];