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

node_modules/is-plain-obj/index.js

@@ -0,0 +1,8 @@
+export default function isPlainObject(value) {
+	if (typeof value !== 'object' || value === null) {
+		return false;
+	}
+
+	const prototype = Object.getPrototypeOf(value);
+	return (prototype === null || prototype === Object.prototype || Object.getPrototypeOf(prototype) === null) && !(Symbol.toStringTag in value) && !(Symbol.iterator in value);
+}