Add reusable two-factor verification for login and money operations (#32)

frontend/app/lib/generated/i18n/app_localizations.dart

@@ -1465,6 +1465,174 @@ abstract class AppLocalizations {
   /// In en, this message translates to:
   /// **'Make another transaction'**
   String get wAnother;
+
+  /// No description provided for @factorTitle.
+  ///
+  /// In en, this message translates to:
+  /// **'One more check.'**
+  String get factorTitle;
+
+  /// No description provided for @factorLogin.
+  ///
+  /// In en, this message translates to:
+  /// **'Confirm it’s you to finish signing in.'**
+  String get factorLogin;
+
+  /// No description provided for @factorMoney.
+  ///
+  /// In en, this message translates to:
+  /// **'Confirm this transaction. No money moves before confirmation.'**
+  String get factorMoney;
+
+  /// No description provided for @factorEnableHelp.
+  ///
+  /// In en, this message translates to:
+  /// **'Confirm to turn on two-factor verification for sign-in and money operations.'**
+  String get factorEnableHelp;
+
+  /// No description provided for @factorDisableHelp.
+  ///
+  /// In en, this message translates to:
+  /// **'Confirm to turn off two-factor verification. Sign-in and money operations will no longer ask for a second code.'**
+  String get factorDisableHelp;
+
+  /// No description provided for @factorEmail.
+  ///
+  /// In en, this message translates to:
+  /// **'Enter the six-digit code sent to your email.'**
+  String get factorEmail;
+
+  /// No description provided for @factorAuthenticator.
+  ///
+  /// In en, this message translates to:
+  /// **'Enter the current six-digit code from your authenticator app.'**
+  String get factorAuthenticator;
+
+  /// No description provided for @factorCode.
+  ///
+  /// In en, this message translates to:
+  /// **'Verification code'**
+  String get factorCode;
+
+  /// No description provided for @factorConfirm.
+  ///
+  /// In en, this message translates to:
+  /// **'Verify and continue'**
+  String get factorConfirm;
+
+  /// No description provided for @factorResend.
+  ///
+  /// In en, this message translates to:
+  /// **'Send a new code'**
+  String get factorResend;
+
+  /// No description provided for @factorHelp.
+  ///
+  /// In en, this message translates to:
+  /// **'Check your inbox and spam folder. A new code replaces the previous one.'**
+  String get factorHelp;
+
+  /// No description provided for @factorAppHelp.
+  ///
+  /// In en, this message translates to:
+  /// **'Use the current code. If you cannot access your authenticator, cancel this action.'**
+  String get factorAppHelp;
+
+  /// No description provided for @factorInvalid.
+  ///
+  /// In en, this message translates to:
+  /// **'That code is not valid. Check all six digits and try again.'**
+  String get factorInvalid;
+
+  /// No description provided for @factorExpired.
+  ///
+  /// In en, this message translates to:
+  /// **'This verification has expired. Request a new code or return to start again.'**
+  String get factorExpired;
+
+  /// No description provided for @factorLocked.
+  ///
+  /// In en, this message translates to:
+  /// **'Too many incorrect attempts. Wait five minutes, then start verification again.'**
+  String get factorLocked;
+
+  /// No description provided for @factorWait.
+  ///
+  /// In en, this message translates to:
+  /// **'Please wait before requesting another code.'**
+  String get factorWait;
+
+  /// No description provided for @factorRequired.
+  ///
+  /// In en, this message translates to:
+  /// **'Verification is needed again. Please confirm this action once more.'**
+  String get factorRequired;
+
+  /// No description provided for @factorUnavailable.
+  ///
+  /// In en, this message translates to:
+  /// **'Could not complete verification. Try again or cancel this action.'**
+  String get factorUnavailable;
+
+  /// No description provided for @factorCooldown.
+  ///
+  /// In en, this message translates to:
+  /// **'Send a new code in {seconds}s'**
+  String factorCooldown(int seconds);
+
+  /// No description provided for @factorSettings.
+  ///
+  /// In en, this message translates to:
+  /// **'Two-factor verification'**
+  String get factorSettings;
+
+  /// No description provided for @factorSettingsHelp.
+  ///
+  /// In en, this message translates to:
+  /// **'Add a verification code when you sign in, top up, exchange or pay out.'**
+  String get factorSettingsHelp;
+
+  /// No description provided for @factorOn.
+  ///
+  /// In en, this message translates to:
+  /// **'On'**
+  String get factorOn;
+
+  /// No description provided for @factorOff.
+  ///
+  /// In en, this message translates to:
+  /// **'Off'**
+  String get factorOff;
+
+  /// No description provided for @factorEnable.
+  ///
+  /// In en, this message translates to:
+  /// **'Turn on'**
+  String get factorEnable;
+
+  /// No description provided for @factorDisable.
+  ///
+  /// In en, this message translates to:
+  /// **'Turn off'**
+  String get factorDisable;
+
+  /// No description provided for @factorEmailMethod.
+  ///
+  /// In en, this message translates to:
+  /// **'Email code'**
+  String get factorEmailMethod;
+
+  /// No description provided for @factorAppMethod.
+  ///
+  /// In en, this message translates to:
+  /// **'Authenticator app'**
+  String get factorAppMethod;
+
+  /// No description provided for @factorAppExpired.
+  ///
+  /// In en, this message translates to:
+  /// **'This verification has expired. Return and start again.'**
+  String get factorAppExpired;
 }
 
 class _AppLocalizationsDelegate