Add CORS testing documentation and HTML test page for Passkey Cross-Device Authentication

Introduce a comprehensive CORS testing guide in CORS_TEST_ANLEITUNG.md, detailing steps for testing OPTIONS and POST requests, along with expected responses. Additionally, add a new HTML test page (test-cors.html) to facilitate interactive testing of CORS headers and responses for the Passkey registration API. Update the server API to ensure proper CORS headers are set for Cross-Device Authentication, enhancing the overall testing and debugging process.

pages/registrieren.vue

@@ -505,8 +505,7 @@ const handleRegisterWithPasskey = async () => {
     const webauthnStart = Date.now()
     
     const mod = await import('@simplewebauthn/browser')
-    // startRegistration erwartet die Options direkt
-    // @simplewebauthn/browser v13+ erwartet die Options direkt
+    // startRegistration erwartet die Options direkt (wie in anderen Dateien auch)
     let credential
     try {
       // Timeout-Warnung nach 2 Minuten
@@ -517,29 +516,11 @@ const handleRegisterWithPasskey = async () => {
         console.warn('[DEBUG] Challenge:', pre.options?.challenge)
       }, 120000)
       
-      // Stelle sicher, dass die Options korrekt formatiert sind
-      // @simplewebauthn/browser v13+ erwartet die Options direkt als Objekt
-      const registrationOptions = {
-        challenge: pre.options.challenge,
-        rp: pre.options.rp,
-        user: pre.options.user,
-        pubKeyCredParams: pre.options.pubKeyCredParams,
-        timeout: pre.options.timeout,
-        attestation: pre.options.attestation || 'none',
-        excludeCredentials: pre.options.excludeCredentials || [],
-        authenticatorSelection: pre.options.authenticatorSelection,
-        extensions: pre.options.extensions || {}
-      }
-      
       console.log('[DEBUG] startRegistration called - QR-Code should appear now (if Cross-Device)')
-      console.log('[DEBUG] Registration options structure:', {
-        hasChallenge: !!registrationOptions.challenge,
-        hasRp: !!registrationOptions.rp,
-        hasUser: !!registrationOptions.user,
-        timeout: registrationOptions.timeout
-      })
+      console.log('[DEBUG] Passing options directly to startRegistration (same as in profil.vue)')
       
-      credential = await mod.startRegistration(registrationOptions)
+      // Direkt die Options übergeben (wie in profil.vue und passkey-wiederherstellen.vue)
+      credential = await mod.startRegistration(pre.options)
       
       clearTimeout(timeoutWarning)