fix(settings): otp nonsync signup redirect fix

[StaberindeZA]

Because

• Firefox non-sync RPs are redirect to Settings and are not signed into the browser, but not sync.

This pull request

• Updates OTP signup for Firefox non-sync RPs so that users are signed into the browser and redirected to the approrpiate page.

Issue that this pull request solves

Closes: #FXA-13114

Checklist

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• My commit is GPG signed.
• If applicable, I have modified or added tests which pass locally.
• I have added necessary documentation (if appropriate).
• I have verified that my changes render correctly in RTL (if appropriate).
• I have manually reviewed all AI generated code.

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