Because:
- Add-passkey kept its own reason map, reporting webauthn_unknown and auth_error_<n>.
- Glean reasons should cover only errors that could drive a product change.
This commit:
- Makes add-passkey report the shared WebAuthn gleanReason.
- Reports server errors as server_error, except errnos 226 and 233.
- Reports a duplicate passkey as not_allowed instead of not_supported.
- Treats only errors from the add-passkey prompt as WebAuthn errors.
- Sends every error that reports 'unexpected' to Sentry.
Closes FXA-14005