Add channel system with CLI, Telegram, and Web channel implementations

Define channel abstractions (IChannel, IChannelManager) with event-driven
message and connection handling. Implement ChannelManager for multi-channel
orchestration, CliChannel for terminal I/O, TelegramChannel with adapter
pattern for bot API integration, and WebChannel stub. Includes DI
registration and channel type enumeration.

Luna.Channels/ChannelManager.cs

@@ -0,0 +1,62 @@
+using System.Collections.Immutable;
+using Luna.Channels.Abstractions;
+using Luna.Core.Abstractions;
+using Microsoft.Extensions.Logging;
+
+namespace Luna.Channels;
+
+public class ChannelManager(ISessionManager sessionManager, ILogger<ChannelManager> logger) : IChannelManager
+{
+    private readonly Dictionary<string, IChannel> channels = new();
+    private readonly Dictionary<string, string> sessionMap = new();
+    
+    public event EventHandler<ChannelMessageReceivedEventArgs>? MessageRouted;
+    
+    public void RegisterChannel(IChannel channel)
+    {
+        if (!channels.TryAdd(channel.ChannelId, channel))
+            throw new InvalidOperationException($"Channel with id {channel.ChannelId} is already registered.");
+
+        channel.MessageReceived += OnMessageReceivedAsync;
+    }
+
+    public void UnregisterChannel(string channelId)
+    {
+        if (!channels.TryGetValue(channelId, out var channel))
+            return;
+
+        channel.MessageReceived -= OnMessageReceivedAsync;
+        channels.Remove(channelId);
+    }
+
+    public IChannel? GetChannel(string channelId)
+    {
+        channels.TryGetValue(channelId, out var channel);
+        return channel;
+    }
+
+    public IReadOnlyList<IChannel> GetAllChannels()
+        => channels.Values.ToImmutableList();
+
+    private async Task OnMessageReceivedAsync(object? sender, ChannelMessageReceivedEventArgs args)
+    {
+        if (args.IsHandled)
+            return;
+        
+        var channel = args.Channel;
+        var message = args.Message;
+        
+        try
+        {
+            var response = sessionManager
+                .RouteMessagesAsync(message.Content, message.ConversationId, channel.ChannelId);
+            
+            await channel.SendStreamingMessageAsync(response);
+            MessageRouted?.Invoke(this, args);
+        }
+        catch (Exception exception)
+        {
+            logger.LogError(exception, "Message routing for channel of type {Type} with id {Id} failed", channel.ChannelType, channel.ChannelId);
+        }
+    }
+}