Because:
- The "Cancel" button on the "Creating passkey…" loading page navigated back
to settings without any feedback. When a credential manager popup (e.g.,
Bitwarden) is dismissed via focus loss, the WebAuthn ceremony stays pending
and Cancel is the user's only escape — but it returned silently, leaving
no confirmation that cancellation was processed.
This commit:
- Shows the standard cancellation banner ("Passkey setup was canceled. Try
again.") in the alert bar before navigating back, mirroring the feedback
the user gets when the ceremony itself reports a cancel/timeout.
Closes #FXA-13681