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

quixzoom-landing-fixed/favicon.svg

@@ -1,4 +1,19 @@
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+<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 512 512">
+  <defs>
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+      <stop offset="0%" stop-color="#0A0A0A"/>
+      <stop offset="100%" stop-color="#1A1A1A"/>
+    </linearGradient>
+    <linearGradient id="qz-accent" x1="0%" y1="0%" x2="100%" y2="100%">
+      <stop offset="0%" stop-color="#0066FF"/>
+      <stop offset="100%" stop-color="#0052CC"/>
+    </linearGradient>
+  </defs>
+  <!-- Background -->
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+  <!-- Camera lens shape -->
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+</svg>