Enhance debug logging for Cross-Device Passkey Registration

Add detailed debug statements in the registrieren.vue component to provide insights into the QR-Code generation process and the Cross-Device authentication flow. Additionally, update the register-passkey API to log request details, including user agent and method, to improve troubleshooting capabilities and ensure clarity during the registration process.

server/api/auth/register-passkey.post.js

@@ -11,12 +11,16 @@ import { assertPasswordNotPwned } from '../../utils/hibp.js'
 export default defineEventHandler(async (event) => {
   const requestStart = Date.now()
   const requestOrigin = getHeader(event, 'origin')
+  const userAgent = getHeader(event, 'user-agent')
   const { origin: webauthnOrigin } = getWebAuthnConfig()
   
   console.log('[DEBUG] register-passkey request received', {
     origin: requestOrigin,
     webauthnOrigin,
-    timestamp: new Date().toISOString()
+    userAgent: userAgent?.substring(0, 100),
+    timestamp: new Date().toISOString(),
+    method: getMethod(event),
+    note: 'Dieser Request sollte vom Smartphone kommen, wenn der QR-Code gescannt wurde'
   })
 
   // CORS-Header für Cross-Device Authentication