feat: enhance user presence and channel interaction features

- Fix userlist not refreshing after creating a new channel.
- Implement unmute timer with a background job to automatically unmute users.
- Improve userlist display by filtering invisible users and ensuring proper transitions between statuses.
- Add clickable usernames, @mentions, and #channels for easier navigation.
- Embed theme colors from source sites for a more cohesive UI.
- Introduce a stateful userlist that updates incrementally via SignalR events.
- Restrict auto-opening of files to safe types only, enhancing security.
- Refactor user management into a dedicated service to reduce code duplication.
- Add a MuteExpirationService to handle timed mutes.
- Update documentation with Mermaid diagrams for major flows.

src/EchoHub.Client/UI/Chat/ChatColors.cs

@@ -13,6 +13,7 @@ public static partial class ChatColors
     public static readonly Attribute SystemAttr = new(new Color(0, 180, 180), Color.None);
     public static readonly Attribute MentionHighlightAttr = new(Color.White, new Color(80, 40, 0));
     public static readonly Attribute MentionTextAttr = new(new Color(255, 180, 50), Color.None);
+    public static readonly Attribute ChannelRefAttr = new(new Color(100, 200, 255), Color.None);
     public static readonly Attribute EmbedBorderAttr = new(new Color(91, 155, 213), Color.None);
     public static readonly Attribute EmbedTitleAttr = new(Color.White, Color.None);
     public static readonly Attribute EmbedDescAttr = new(new Color(160, 160, 160), Color.None);
@@ -21,8 +22,8 @@ public static partial class ChatColors
     public static readonly Attribute FileAttr = new(new Color(100, 180, 255), Color.None);
 
     /// <summary>
-    /// Split text around @mentions, giving each @word the MentionTextAttr accent color.
-    /// Non-mention text uses the provided default color.
+    /// Split text around @mentions and #channels, giving each the appropriate accent color.
+    /// Non-special text uses the provided default color.
     /// </summary>
     public static List<ChatSegment> SplitMentions(string text, Attribute? defaultColor = null)
     {
@@ -38,12 +39,40 @@ public static partial class ChatColors
             lastIndex = match.Index + match.Length;
         }
 
-        if (lastIndex < text.Length)
-            segments.Add(new ChatSegment(text[lastIndex..], defaultColor));
+        // Second pass: highlight #channels in non-mention segments
+        var mentionSegments = segments;
+        segments = [];
+        foreach (var seg in mentionSegments)
+        {
+            if (seg.Color != null && seg.Color != defaultColor)
+            {
+                // Already colored (mention) — keep as-is
+                segments.Add(seg);
+                continue;
+            }
+
+            int segLast = 0;
+            foreach (Match match in ChannelRefRegex().Matches(seg.Text))
+            {
+                if (match.Index > segLast)
+                    segments.Add(new ChatSegment(seg.Text[segLast..match.Index], defaultColor));
+
+                segments.Add(new ChatSegment(match.Value, ChannelRefAttr));
+                segLast = match.Index + match.Length;
+            }
+
+            if (segLast < seg.Text.Length)
+                segments.Add(new ChatSegment(seg.Text[segLast..], defaultColor));
+        }
 
         return segments;
     }
 
-    [GeneratedRegex(@"@[\w-]+")]
+    // @mention — not preceded by a word char (avoids emails)
+    [GeneratedRegex(@"(?<!\w)@[\w-]+")]
     private static partial Regex MentionRegex();
+
+    // #channel — not preceded by a word char, must contain at least one letter (avoids hex colors / issue numbers)
+    [GeneratedRegex(@"(?<!\w)#(?=.*[a-zA-Z])[\w-]+")]
+    private static partial Regex ChannelRefRegex();
 }

src/EchoHub.Client/UI/Chat/ChatLine.cs

@@ -19,6 +19,7 @@ public partial class ChatLine
     public string? AttachmentUrl { get; set; }
     public string? AttachmentFileName { get; set; }
     public MessageType? Type { get; set; }
+    public string? SenderUsername { get; set; }
     /// <summary>Number of spaces to prepend on continuation lines when this line is word-wrapped.</summary>
     public int ContinuationIndent { get; set; }
 
@@ -118,13 +119,14 @@ public partial class ChatLine
         if (results.Count == 0)
             return [this];
 
-        // Propagate attachment/type metadata to all wrapped lines so they remain clickable
+        // Propagate metadata to all wrapped lines so they remain clickable
         foreach (var wrapped in results)
         {
             wrapped.AttachmentUrl = AttachmentUrl;
             wrapped.AttachmentFileName = AttachmentFileName;
             wrapped.Type = Type;
             wrapped.MessageId = MessageId;
+            wrapped.SenderUsername = SenderUsername;
         }
 
         return results;

src/EchoHub.Client/UI/Chat/ChatMessageManager.cs

@@ -272,7 +272,10 @@ public sealed class ChatMessageManager
         }
 
         foreach (var line in lines)
+        {
             line.MessageId = message.Id;
+            line.SenderUsername = message.SenderUsername;
+        }
 
         if (!string.IsNullOrEmpty(_currentUser) && message.Type == MessageType.Text)
         {
@@ -329,18 +332,20 @@ public sealed class ChatMessageManager
         int textWidth = chatWidth - indentCols - borderCols;
         if (textWidth < 20) textWidth = 20;
 
+        var borderAttr = HexColorHelper.ParseHexColor(embed.ThemeColor) ?? ChatColors.EmbedBorderAttr;
+
         void AddTextLine(string text, Attribute? color)
         {
             lines.Add(new ChatLine(
             [
                 new ChatSegment(indent, null),
-                new ChatSegment(border, ChatColors.EmbedBorderAttr),
+                new ChatSegment(border, borderAttr),
                 new ChatSegment(text, color)
             ]));
         }
 
         if (!string.IsNullOrWhiteSpace(embed.SiteName))
-            AddTextLine(embed.SiteName, ChatColors.EmbedBorderAttr);
+            AddTextLine(embed.SiteName, borderAttr);
 
         if (!string.IsNullOrWhiteSpace(embed.Title))
         {

src/EchoHub.Client/UI/ListSources/UserListSource.cs

@@ -12,14 +12,14 @@ namespace EchoHub.Client.UI.ListSources;
 /// </summary>
 public class UserListSource : IListDataSource
 {
-    private readonly List<(string Text, Attribute? NameColor)> _users = [];
+    private readonly List<(string Text, Attribute? NameColor, string Username)> _users = [];
 
     public event NotifyCollectionChangedEventHandler? CollectionChanged;
     public int Count => _users.Count;
     public int MaxItemLength { get; private set; }
     public bool SuspendCollectionChangedEvent { get; set; }
 
-    public void Update(List<(string Text, Attribute? NameColor)> users)
+    public void Update(List<(string Text, Attribute? NameColor, string Username)> users)
     {
         _users.Clear();
         _users.AddRange(users);
@@ -28,15 +28,18 @@ public class UserListSource : IListDataSource
             CollectionChanged?.Invoke(this, new NotifyCollectionChangedEventArgs(NotifyCollectionChangedAction.Reset));
     }
 
+    public string? GetUsername(int index) =>
+        index >= 0 && index < _users.Count ? _users[index].Username : null;
+
     public bool IsMarked(int item) => false;
     public void SetMark(int item, bool value) { }
-    public IList ToList() => _users.Select(u => u.Text).ToList();
+    public IList ToList() => _users.Select(u => (object)u.Text).ToList();
 
     public void Render(ListView listView, bool selected, int item, int col, int row, int width, int viewportX = 0)
     {
         listView.Move(Math.Max(col - viewportX, 0), row);
 
-        var (text, nameColor) = _users[item];
+        var (text, nameColor, _) = _users[item];
         var normalAttr = listView.GetAttributeForRole(selected ? VisualRole.Focus : VisualRole.Normal);
 
         // Find where the name starts (after status icon + space + optional role badge)

src/EchoHub.Client/UI/MainWindow.cs

@@ -1,3 +1,4 @@
+using System.Text.RegularExpressions;
 using EchoHub.Client.Services;
 using EchoHub.Client.Themes;
 using EchoHub.Client.UI.Chat;
@@ -19,7 +20,7 @@ namespace EchoHub.Client.UI;
 /// <summary>
 /// Main Terminal.Gui window for the EchoHub chat client.
 /// </summary>
-public sealed class MainWindow : Runnable
+public sealed partial class MainWindow : Runnable
 {
     private readonly IApplication _app;
     private readonly ListView _channelList;
@@ -140,6 +141,16 @@ public sealed class MainWindow : Runnable
     /// </summary>
     public event Action<string, string>? OnFileDownloadRequested;
 
+    /// <summary>
+    /// Fired when the user activates a username (in userlist or message). Parameter is the username.
+    /// </summary>
+    public event Action<string>? OnUserProfileRequested;
+
+    /// <summary>
+    /// Fired when the user activates a #channel reference in a message. Parameter is the channel name.
+    /// </summary>
+    public event Action<string>? OnChannelJoinRequested;
+
     public MainWindow(IApplication app, ChatMessageManager messageManager)
     {
         _app = app;
@@ -250,6 +261,7 @@ public sealed class MainWindow : Runnable
         };
         _usersListSource = new UserListSource();
         _usersList.Source = _usersListSource;
+        _usersList.Accepting += OnUsersListAccepting;
         _usersFrame.Add(_usersList);
         Add(_usersFrame);
 
@@ -410,17 +422,66 @@ public sealed class MainWindow : Runnable
             return;
 
         var line = source.GetLine(index.Value);
-        if (line?.AttachmentUrl is null || line.AttachmentFileName is null)
-            return;
+        if (line is null) return;
 
-        if (line.Type == MessageType.Audio)
+        // Audio/file attachments take priority
+        if (line.AttachmentUrl is not null && line.AttachmentFileName is not null)
         {
-            OnAudioPlayRequested?.Invoke(line.AttachmentUrl, line.AttachmentFileName);
+            if (line.Type == MessageType.Audio)
+            {
+                OnAudioPlayRequested?.Invoke(line.AttachmentUrl, line.AttachmentFileName);
+                e.Handled = true;
+                return;
+            }
+
+            if (line.Type == MessageType.File)
+            {
+                OnFileDownloadRequested?.Invoke(line.AttachmentUrl, line.AttachmentFileName);
+                e.Handled = true;
+                return;
+            }
+        }
+
+        var lineText = line.ToString();
+
+        // Check for @mention — open mentioned user's profile
+        // Negative lookbehind prevents matching emails (user@domain)
+        var mentionMatch = ClickMentionRegex().Match(lineText);
+        if (mentionMatch.Success)
+        {
+            OnUserProfileRequested?.Invoke(mentionMatch.Groups[1].Value);
+            e.Handled = true;
+            return;
+        }
+
+        // Check for #channel — join/switch to that channel
+        // Require at least one letter to avoid matching hex colors (#ff0000) or issue numbers (#123)
+        var channelMatch = ClickChannelRegex().Match(lineText);
+        if (channelMatch.Success)
+        {
+            OnChannelJoinRequested?.Invoke(channelMatch.Groups[1].Value);
+            e.Handled = true;
+            return;
+        }
+
+        // Default: open sender's profile
+        if (line.SenderUsername is not null)
+        {
+            OnUserProfileRequested?.Invoke(line.SenderUsername);
             e.Handled = true;
         }
-        else if (line.Type == MessageType.File)
+    }
+
+    private void OnUsersListAccepting(object? sender, CommandEventArgs e)
+    {
+        var index = _usersList.SelectedItem;
+        if (!index.HasValue || index.Value < 0 || index.Value >= _usersListSource.Count)
+            return;
+
+        var username = _usersListSource.GetUsername(index.Value);
+        if (username is not null)
         {
-            OnFileDownloadRequested?.Invoke(line.AttachmentUrl, line.AttachmentFileName);
+            OnUserProfileRequested?.Invoke(username);
             e.Handled = true;
         }
     }
@@ -862,14 +923,14 @@ public sealed class MainWindow : Runnable
             var name = u.DisplayName ?? u.Username;
             var roleTag = u.Role switch
             {
-                ServerRole.Owner => "\u2605", // ★
-                ServerRole.Admin => "\u2666", // ♦
-                ServerRole.Mod => "\u2740",   // ❀
+                ServerRole.Owner => "\u2605 ", // ★
+                ServerRole.Admin => "\u2666 ", // ♦
+                ServerRole.Mod => "\u2740 ",   // ❀
                 _ => ""
             };
             var text = $"{statusIcon} {roleTag}{name}";
             var nameColor = HexColorHelper.ParseHexColor(u.NicknameColor);
-            return (text, nameColor);
+            return (text, nameColor, u.Username);
         }).ToList();
 
         _usersListSource.Update(displayItems);
@@ -877,4 +938,11 @@ public sealed class MainWindow : Runnable
         _usersFrame.Title = $"Users ({users.Count})";
     }
 
+    // @mention — not preceded by a word char (avoids emails)
+    [GeneratedRegex(@"(?<!\w)@([\w-]+)")]
+    private static partial Regex ClickMentionRegex();
+
+    // #channel — not preceded by a word char, must contain at least one letter (avoids hex colors / issue numbers)
+    [GeneratedRegex(@"(?<!\w)#((?=.*[a-zA-Z])[\w-]+)")]
+    private static partial Regex ClickChannelRegex();
 }