feat(login-compact): implement bunker signer with nostrconnect:// QR code

- Generate nostrconnect:// URI and display as scannable QR code
- Tapping QR opens the URI for signer apps that register as handlers
- Allow manual bunker:// URI entry with connect button
- Stop nostrconnect:// listener when bunker:// connection is used
- Add props: nostrConnectRelay, appName, appIcon for customization
- Clean up signer on component destroy

Author: pablof7z