feat: implement background update check and add version notification in AppOrchestrator

src/EchoHub.Client/AppOrchestrator.cs

@@ -414,6 +414,18 @@ public sealed class AppOrchestrator : IDisposable
 
             FetchAndUpdateOnlineUsers();
             SaveServerToConfig(result);
+
+            // Check for newer version in the background
+            _ = Task.Run(async () =>
+            {
+                var newVersion = await UpdateChecker.CheckForUpdateAsync();
+                if (newVersion is not null)
+                {
+                    InvokeUI(() => _mainWindow.AddSystemMessage(
+                        HubConstants.DefaultChannel,
+                        $"A new version of EchoHub is available: v{newVersion} (current: v{MainWindow.AppVersion}). Visit https://github.com/HueByte/EchoHub/releases"));
+                }
+            });
         }, "Connection failed", "Connect");
     }
 

src/EchoHub.Client/Services/UpdateChecker.cs

@@ -0,0 +1,47 @@
+using System.Net.Http.Json;
+using System.Text.Json.Serialization;
+
+namespace EchoHub.Client.Services;
+
+public static class UpdateChecker
+{
+    private static readonly Uri ReleaseUrl =
+        new("https://api.github.com/repos/HueByte/EchoHub/releases/latest");
+
+    /// <summary>
+    /// Checks GitHub for a newer release. Returns the new version string if one exists, or null.
+    /// Never throws — all errors are silently swallowed.
+    /// </summary>
+    public static async Task<string?> CheckForUpdateAsync()
+    {
+        try
+        {
+            using var http = new HttpClient { Timeout = TimeSpan.FromSeconds(5) };
+            http.DefaultRequestHeaders.UserAgent.ParseAdd("EchoHub-Client");
+
+            var release = await http.GetFromJsonAsync<GitHubRelease>(ReleaseUrl);
+            if (release?.TagName is null)
+                return null;
+
+            var tag = release.TagName.TrimStart('v', 'V');
+            if (!Version.TryParse(tag, out var latest))
+                return null;
+
+            var currentStr = typeof(UpdateChecker).Assembly.GetName().Version?.ToString(3);
+            if (currentStr is null || !Version.TryParse(currentStr, out var current))
+                return null;
+
+            return latest > current ? tag : null;
+        }
+        catch
+        {
+            return null;
+        }
+    }
+
+    private sealed class GitHubRelease
+    {
+        [JsonPropertyName("tag_name")]
+        public string? TagName { get; set; }
+    }
+}

src/EchoHub.Client/UI/MainWindow.cs

@@ -34,7 +34,7 @@ public sealed class MainWindow : Runnable
     private const int UsersPanelWidth = 22;
     private static readonly Key F2Key = Key.F2;
 
-    private static readonly string AppVersion =
+    internal static readonly string AppVersion =
         typeof(MainWindow).Assembly.GetName().Version?.ToString(3) ?? "?";
 
     // Cached Key constants — compare via .KeyCode to avoid Key.Equals (which also checks Handled)
@@ -479,19 +479,33 @@ public sealed class MainWindow : Runnable
     /// </summary>
     public void AddSystemMessage(string channelName, string text)
     {
-        var time = DateTimeOffset.Now.ToString("HH:mm");
-        var segments = new List<ChatSegment>
-        {
-            new($"[{time}] ", ChatColors.TimestampAttr),
-            new($"** {text}", ChatColors.SystemAttr)
-        };
-
         if (!_channelMessages.TryGetValue(channelName, out var messages))
         {
             messages = [];
             _channelMessages[channelName] = messages;
         }
-        messages.Add(new ChatLine(segments));
+
+        var time = DateTimeOffset.Now.ToString("HH:mm");
+        var textLines = text.Split('\n');
+
+        // First line gets timestamp prefix
+        messages.Add(new ChatLine(
+        [
+            new($"[{time}] ", ChatColors.TimestampAttr),
+            new($"** {textLines[0].TrimEnd('\r')}", ChatColors.SystemAttr)
+        ]));
+
+        // Continuation lines are indented to align
+        var indent = new string(' ', $"[{time}] ** ".Length);
+        for (int i = 1; i < textLines.Length; i++)
+        {
+            var line = textLines[i].TrimEnd('\r');
+            if (string.IsNullOrWhiteSpace(line)) continue;
+            messages.Add(new ChatLine(
+            [
+                new($"{indent}{line}", ChatColors.SystemAttr)
+            ]));
+        }
 
         if (channelName == _currentChannel)
         {