feat(signin): add "Forgot password?" link to the passkey password fallback
Because: - Passkey users entering their password on the fallback screen had no reset path when they can't recall it. Because reset risks Sync data loss, it is offered only as a last resort, after they exhaust their attempts. This commit: - Adds a throttle-gated "Forgot password?" link to the passkey password fallback screen, shown only after a throttling (errno 114) error. Closes #FXA-14170