feat: Passwordless cross-device authentication

- Arkitektur: docs/auth/passwordless-architecture.md
- Backend: iom/quixzoom-auth-service/ (FastAPI + Redis)
- Webb: quixzoom-market-pages/se/login/ (QR-kod + polling)
- App: iom/quixzoom-app/src/features/auth/ (push + deep links)

Flöde: QR-kod → app-godkännande → webb-inloggad

landvex-master-api/node_modules/xtend/mutable.js

@@ -0,0 +1,17 @@
+module.exports = extend
+
+var hasOwnProperty = Object.prototype.hasOwnProperty;
+
+function extend(target) {
+    for (var i = 1; i < arguments.length; i++) {
+        var source = arguments[i]
+
+        for (var key in source) {
+            if (hasOwnProperty.call(source, key)) {
+                target[key] = source[key]
+            }
+        }
+    }
+
+    return target
+}