Implement NotifyOnStatusChange feature for nodes and enhance Telegram notifications

- Added `NotifyOnStatusChange` property to the `Node` class and related DTOs to allow individual node configuration for status change notifications.
- Updated `NodeHealthCheckService` to send Telegram notifications to admins when a node's status changes, based on the new property.
- Enhanced the `ITelegramNotifier` interface with a method for notifying admins about node status changes.
- Modified the frontend to include a checkbox for `NotifyOnStatusChange` in the node editing dialog, allowing admins to easily configure this setting.
- Updated API documentation to reflect the new `notifyOnStatusChange` parameter in the node update endpoint.
- Added tests to ensure the correct behavior of the new feature and its integration with existing functionality.

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

@@ -55,6 +55,7 @@ public static class NodeEndpoints
             body.BaseAddress,
             body.Location,
             body.IsEnabled,
+            body.NotifyOnStatusChange,
             body.Username,
             body.Password
         );
@@ -98,6 +99,7 @@ public sealed record UpdateNodeBody(
     string BaseAddress,
     string? Location,
     bool IsEnabled,
+    bool NotifyOnStatusChange,
     string? Username,
     string? Password
 );

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

@@ -1,6 +1,7 @@
 using Microsoft.Extensions.Options;
 using PnvPanel.Application.Common.Interfaces;
 using PnvPanel.Domain.Billing;
+using PnvPanel.Domain.Nodes;
 using PnvPanel.Domain.Support;
 using PnvPanel.Infrastructure.Telegram;
 using Telegram.Bot;
@@ -358,6 +359,48 @@ internal sealed class TelegramNotifier(
         }
     }
 
+    public async Task NotifyAdminsNodeStatusChangedAsync(
+        Guid nodeId,
+        string nodeName,
+        NodeStatus status,
+        CancellationToken cancellationToken
+    )
+    {
+        if (string.IsNullOrWhiteSpace(options.Value.BotToken))
+            return;
+
+        var emoji = status == NodeStatus.Online ? "✅" : "🔴";
+        var statusLabel = status == NodeStatus.Online ? "снова в сети" : "недоступна";
+        var text = $"{emoji} Нода <b>{Escape(nodeName)}</b> {statusLabel}.";
+
+        InlineKeyboardMarkup? keyboard = null;
+        if (!string.IsNullOrWhiteSpace(options.Value.PublicSiteUrl))
+        {
+            var url = $"{options.Value.PublicSiteUrl.TrimEnd('/')}/admin/nodes";
+            keyboard = new InlineKeyboardMarkup(
+                new[] { InlineKeyboardButton.WithUrl("🌐 Открыть на сайте", url) }
+            );
+        }
+
+        foreach (var adminId in options.Value.ParseAdminTelegramUserIds())
+        {
+            try
+            {
+                await botClient.SendMessage(
+                    adminId,
+                    text,
+                    parseMode: ParseMode.Html,
+                    replyMarkup: keyboard,
+                    cancellationToken: cancellationToken
+                );
+            }
+            catch
+            {
+                // Админ мог не запускать бота (нет чата с ботом) — пропускаем, не валим команду.
+            }
+        }
+    }
+
     private static string Escape(string text) =>
         text.Replace("&", "&amp;").Replace("<", "&lt;").Replace(">", "&gt;");
 }