Enable automatic biometric presentation in iOSNativeLoginTemplate

[sfdctaka]

Summary

• Sets biometricAuthenticationManager().automaticPresentation = true in SceneDelegate of iOSNativeLoginTemplate
  so the SDK drives the biometric flow automatically.
• Demonstrates usage of automaticPresentation.

Test plan

• Generate an app from iOSNativeLoginTemplate and confirm it builds (./test_template.sh --template iOSNativeLoginTemplate --platform ios).
• Run the generated app, log in, and verify the biometric opt-in dialog is presented automatically.
• Opt in, background/lock the app, and verify the biometric unlock prompt is auto-triggered on resume.

[wmathurin]

👍