Gerneate qr code

[Wuuuuu5]

Adds a QR code generator to the admin dashboard. Generates a random browser-safe token and renders it as a scannable QR code image using the qrcode package.

• Token generation is currently client-side only — no signing, no expiry, no server-side persistence yet. This covers the QR rendering mechanic; wiring it to a real signed/time-limited token is separate follow-up work.