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.

backend/src/PnvPanel.Api/Endpoints/AuthEndpoints.cs

@@ -1,6 +1,7 @@
 using PnvPanel.Api.Common;
 using PnvPanel.Application.Auth;
 using PnvPanel.Application.Auth.ChangePassword;
+using PnvPanel.Application.Auth.ChangeUserName;
 using PnvPanel.Application.Auth.DeleteMyAccount;
 using PnvPanel.Application.Auth.Login;
 using PnvPanel.Application.Auth.Logout;
@@ -26,6 +27,7 @@ public static class AuthEndpoints
         group.MapPost("/refresh", Refresh).Produces<AuthResponseDto>();
         group.MapPost("/logout", Logout).RequireAuthorization().Produces(StatusCodes.Status204NoContent);
         group.MapPost("/change-password", ChangePassword).RequireAuthorization().Produces(StatusCodes.Status204NoContent);
+        group.MapPost("/change-username", ChangeUserName).RequireAuthorization().Produces(StatusCodes.Status204NoContent);
         group.MapGet("/me", Me).RequireAuthorization().Produces<CurrentUserDto>();
         group.MapDelete("/me", DeleteMe).RequireAuthorization().Produces(StatusCodes.Status204NoContent);
 
@@ -82,6 +84,12 @@ public static class AuthEndpoints
         return result.ToHttpResult();
     }
 
+    private static async Task<IResult> ChangeUserName(ChangeUserNameCommand command, ISender sender, CancellationToken cancellationToken)
+    {
+        var result = await sender.Send(command, cancellationToken);
+        return result.ToHttpResult();
+    }
+
     private static async Task<IResult> Me(ISender sender, CancellationToken cancellationToken)
     {
         var result = await sender.Send(new GetCurrentUserQuery(), cancellationToken);

backend/src/PnvPanel.Api/Telegram/PnvBotUpdateHandler.cs

@@ -70,7 +70,7 @@ public sealed class PnvBotUpdateHandler(
             else if (payload.StartsWith("login_", StringComparison.Ordinal))
                 await HandleLoginPromptAsync(botClient, services, chatId, fromId.Value, payload[6..], cancellationToken);
             else
-                await SendWelcomeAsync(botClient, chatId, cancellationToken);
+                await SendWelcomeAsync(botClient, services, chatId, fromId.Value, cancellationToken);
 
             return;
         }
@@ -87,7 +87,7 @@ public sealed class PnvBotUpdateHandler(
                 await HandleRequestsAsync(botClient, services, chatId, fromId.Value, cancellationToken);
                 break;
             case "/help":
-                await SendWelcomeAsync(botClient, chatId, cancellationToken);
+                await SendWelcomeAsync(botClient, services, chatId, fromId.Value, cancellationToken);
                 break;
             default:
                 await botClient.SendMessage(chatId, "Не понимаю эту команду. /help — список команд.", cancellationToken: cancellationToken);
@@ -104,6 +104,12 @@ public sealed class PnvBotUpdateHandler(
         if (data is null || chatId is null)
             return;
 
+        if (data == "reg:new")
+        {
+            await HandleRegisterCallbackAsync(botClient, services, chatId.Value, fromId, callback.From.Username, callback.Id, cancellationToken);
+            return;
+        }
+
         var parts = data.Split(':');
         if (parts.Length != 3 || !Guid.TryParse(parts[2], out var requestId))
             return;
@@ -159,10 +165,19 @@ public sealed class PnvBotUpdateHandler(
                 var linkResult = await sender.Send(new GetConfigLinkQuery(requestId), cancellationToken);
                 await botClient.AnswerCallbackQuery(callback.Id, cancellationToken: cancellationToken);
 
-                await botClient.SendMessage(
-                    chatId.Value,
-                    linkResult.IsSuccess ? linkResult.Value.ConnectionString : $"Не удалось получить ссылку: {linkResult.Error.Message}",
-                    cancellationToken: cancellationToken);
+                if (!linkResult.IsSuccess)
+                {
+                    await botClient.SendMessage(chatId.Value, $"Не удалось получить ссылку: {linkResult.Error.Message}", cancellationToken: cancellationToken);
+                    return;
+                }
+
+                // Редактируем то же сообщение (не плодим отдельное с сырым URL) — ссылка моноширинным
+                // блоком, по нему в Telegram можно тапнуть и скопировать целиком одним движением.
+                var originalText = callback.Message?.Text ?? "";
+                var text = $"{Escape(originalText)}\n\n<code>{Escape(linkResult.Value.ConnectionString)}</code>";
+
+                if (callback.Message is not null)
+                    await botClient.EditMessageText(chatId.Value, callback.Message.Id, text, parseMode: ParseMode.Html, cancellationToken: cancellationToken);
 
                 break;
             }
@@ -196,7 +211,10 @@ public sealed class PnvBotUpdateHandler(
         var userId = await identityService.FindUserIdByTelegramUserIdAsync(fromId, cancellationToken);
         if (userId is null)
         {
-            await botClient.SendMessage(chatId, NotLinkedMessage, cancellationToken: cancellationToken);
+            await botClient.SendMessage(
+                chatId, NotLinkedMessage,
+                replyMarkup: new InlineKeyboardMarkup(new[] { InlineKeyboardButton.WithCallbackData("📝 Зарегистрироваться", "reg:new") }),
+                cancellationToken: cancellationToken);
             return;
         }
 
@@ -216,7 +234,10 @@ public sealed class PnvBotUpdateHandler(
     {
         if (!await TrySetCurrentUserAsync(services, fromId, cancellationToken))
         {
-            await botClient.SendMessage(chatId, NotLinkedMessage, cancellationToken: cancellationToken);
+            await botClient.SendMessage(
+                chatId, NotLinkedMessage,
+                replyMarkup: new InlineKeyboardMarkup(new[] { InlineKeyboardButton.WithCallbackData("📝 Зарегистрироваться", "reg:new") }),
+                cancellationToken: cancellationToken);
             return;
         }
 
@@ -289,16 +310,53 @@ public sealed class PnvBotUpdateHandler(
         }
     }
 
-    private static async Task SendWelcomeAsync(ITelegramBotClient botClient, long chatId, CancellationToken cancellationToken)
+    private static async Task SendWelcomeAsync(
+        ITelegramBotClient botClient, IServiceProvider services, long chatId, long fromId, CancellationToken cancellationToken)
     {
         const string text = "Привет! Это бот PnvPanel.\n\n"
             + "/configs — мои конфиги\n"
             + "Вход без пароля запускается кнопкой «Войти через Telegram» на сайте — бот пришлёт запрос на подтверждение.\n"
             + "/unlink — отвязать Telegram\n"
             + "/help — эта справка";
-        await botClient.SendMessage(chatId, text, cancellationToken: cancellationToken);
+
+        var identityService = services.GetRequiredService<IIdentityService>();
+        var userId = await identityService.FindUserIdByTelegramUserIdAsync(fromId, cancellationToken);
+
+        // Уже привязанным аккаунту предлагать регистрацию незачем.
+        var keyboard = userId is null
+            ? new InlineKeyboardMarkup(new[] { InlineKeyboardButton.WithCallbackData("📝 Зарегистрироваться", "reg:new") })
+            : null;
+
+        await botClient.SendMessage(chatId, text, replyMarkup: keyboard, cancellationToken: cancellationToken);
     }
 
+    private static async Task HandleRegisterCallbackAsync(
+        ITelegramBotClient botClient, IServiceProvider services, long chatId, long fromId, string? username, string callbackId,
+        CancellationToken cancellationToken)
+    {
+        var sender = services.GetRequiredService<ISender>();
+        var result = await sender.Send(new RegisterViaTelegramCommand(fromId, username), cancellationToken);
+
+        await botClient.AnswerCallbackQuery(callbackId, cancellationToken: cancellationToken);
+
+        if (!result.IsSuccess)
+        {
+            await botClient.SendMessage(chatId, $"Не удалось зарегистрироваться: {result.Error.Message}", cancellationToken: cancellationToken);
+            return;
+        }
+
+        var text = "✅ Аккаунт создан.\n\n"
+            + $"Логин: <code>{result.Value.UserName}</code>\n"
+            + $"Пароль: <code>{result.Value.Password}</code>\n\n"
+            + "Сохраните пароль — он присылается только один раз. Логин можно сменить в Настройках на сайте.\n\n"
+            + "Дальше нужно дождаться активации администратором — после неё будут доступны конфиги. "
+            + "Входить можно как по паролю, так и кнопкой «Войти через Telegram».";
+
+        await botClient.SendMessage(chatId, text, parseMode: ParseMode.Html, cancellationToken: cancellationToken);
+    }
+
+    private static string Escape(string text) => text.Replace("&", "&amp;").Replace("<", "&lt;").Replace(">", "&gt;");
+
     private static async Task<bool> TrySetCurrentUserAsync(IServiceProvider services, long telegramUserId, CancellationToken cancellationToken)
     {
         var identityService = services.GetRequiredService<IIdentityService>();