feat: Add app testing registration page

app.js

@@ -363,6 +363,49 @@ document.addEventListener('DOMContentLoaded', () => {
         });
     }
 
+    // --- Tester Registration Logic ---
+    const testerForm = document.getElementById('tester-form');
+    if (testerForm) {
+        testerForm.addEventListener('submit', async (e) => {
+            e.preventDefault();
+            
+            const emailInput = document.getElementById('tester-email');
+            const submitBtn = document.getElementById('tester-submit-btn');
+            const successMsg = document.getElementById('tester-success-msg');
+            const errorMsg = document.getElementById('tester-error-msg');
+            
+            submitBtn.disabled = true;
+            submitBtn.textContent = 'Wird gesendet...';
+            successMsg.style.display = 'none';
+            errorMsg.style.display = 'none';
+            
+            try {
+                const response = await fetch('tester_backend.php', {
+                    method: 'POST',
+                    headers: { 'Content-Type': 'application/json' },
+                    body: JSON.stringify({ email: emailInput.value })
+                });
+                
+                const result = await response.json();
+                
+                if (result.success) {
+                    successMsg.style.display = 'block';
+                    testerForm.reset();
+                } else {
+                    errorMsg.innerHTML = '<i class="fa-solid fa-triangle-exclamation"></i> ' + (result.error || 'Unbekannter Fehler');
+                    errorMsg.style.display = 'block';
+                }
+            } catch (err) {
+                console.error(err);
+                errorMsg.innerHTML = '<i class="fa-solid fa-triangle-exclamation"></i> Netzwerkfehler. Bitte später erneut versuchen.';
+                errorMsg.style.display = 'block';
+            } finally {
+                submitBtn.disabled = false;
+                submitBtn.textContent = 'Als Tester anmelden';
+            }
+        });
+    }
+
     // --- Modal Management for Impressum & Privacy ---
     const modalTriggers = document.querySelectorAll('.legal-trigger');
     const modals = document.querySelectorAll('.modal-overlay');