Implement username change functionality and enhance Telegram bot registration flow

- Added a new endpoint for changing usernames, allowing users to update their login credentials via the API.
- Integrated username change functionality into the settings page, providing a user-friendly interface for this action.
- Enhanced the Telegram bot to support user registration directly through the bot, including username generation and password delivery.
- Updated documentation to reflect the new username change endpoint and registration flow through the Telegram bot.

frontend/src/shared/lib/i18n.ts

@@ -124,6 +124,10 @@ const resources = {
         currentPasswordInvalid: 'Неверный текущий пароль.',
         newPassword: 'Новый пароль',
         passwordChanged: 'Пароль изменён.',
+        changeUserName: 'Сменить логин',
+        changeUserNameHint: 'Текущий логин: {{current}}.',
+        newUserName: 'Новый логин',
+        userNameChanged: 'Логин изменён.',
         telegramHint: 'Привязка Telegram нужна для входа без пароля и восстановления доступа.',
         telegramLinkedStatus: 'Привязан',
         link: 'Привязать Telegram',
@@ -391,6 +395,10 @@ const resources = {
         currentPasswordInvalid: 'Current password is incorrect.',
         newPassword: 'New password',
         passwordChanged: 'Password changed.',
+        changeUserName: 'Change username',
+        changeUserNameHint: 'Current username: {{current}}.',
+        newUserName: 'New username',
+        userNameChanged: 'Username changed.',
         telegramHint: 'Linking Telegram enables passwordless login and account recovery.',
         telegramLinkedStatus: 'Linked',
         link: 'Link Telegram',