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.Abstractions/ChannelConnectionEventArgs.cs

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+namespace Luna.Channels.Abstractions;
+
+/// <summary>
+/// Event arguments for channel connection state changes
+/// </summary>
+public class ChannelConnectionEventArgs : EventArgs
+{
+    /// <summary>
+    /// The channel whose connection state changed
+    /// </summary>
+    public required IChannel Channel { get; init; }
+
+    /// <summary>
+    /// The previous connection state
+    /// </summary>
+    public bool WasConnected { get; init; }
+
+    /// <summary>
+    /// The new connection state
+    /// </summary>
+    public bool IsConnected { get; init; }
+
+    /// <summary>
+    /// Optional error message if connection failed
+    /// </summary>
+    public string? ErrorMessage { get; init; }
+}

Luna.Channels.Abstractions/ChannelMessageReceivedEventArgs.cs

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+using Luna.Shared;
+
+namespace Luna.Channels.Abstractions;
+
+/// <summary>
+/// Event arguments for when a message is received from a channel
+/// </summary>
+public class ChannelMessageReceivedEventArgs : EventArgs
+{
+    /// <summary>
+    /// The received message
+    /// </summary>
+    public required ChannelMessage Message { get; init; }
+
+    /// <summary>
+    /// The channel that received the message
+    /// </summary>
+    public required IChannel Channel { get; init; }
+
+    /// <summary>
+    /// Set to true to indicate the message has been handled and should not be processed further
+    /// </summary>
+    public bool IsHandled { get; set; }
+
+}

Luna.Channels.Abstractions/ChannelType.cs

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+namespace Luna.Channels.Abstractions;
+
+public static class ChannelType
+{
+    public const string Cli = "cli";
+    public const string Web = "web";
+    public const string Telegram = "telegram"; 
+}

Luna.Channels.Abstractions/IChannel.cs

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+using Luna.Shared;
+
+namespace Luna.Channels.Abstractions;
+
+public delegate Task ChannelMessageReceivedEventHandler(object? sender, ChannelMessageReceivedEventArgs args);
+public delegate Task ChannelConnectionChangedEventHandler(object? sender, ChannelConnectionEventArgs args);
+
+/// <summary>
+/// Represents a communication channel for the Luna AI Assistant.
+/// Channels handle sending and receiving messages via different platforms
+/// (e.g., CLI, Telegram, Discord, Email).
+/// </summary>
+public interface IChannel : IDisposable
+{
+    /// <summary>
+    /// Unique identifier for this channel instance
+    /// </summary>
+    string ChannelId { get; }
+
+    /// <summary>
+    /// Type of channel (e.g., "cli", "telegram", "discord")
+    /// </summary>
+    string ChannelType { get; }
+
+    /// <summary>
+    /// Display name for the channel
+    /// </summary>
+    string DisplayName { get; }
+
+    /// <summary>
+    /// Indicates whether the channel is currently connected and ready
+    /// </summary>
+    bool IsConnected { get; }
+
+    /// <summary>
+    /// Event raised when a message is received from the channel
+    /// </summary>
+    event ChannelMessageReceivedEventHandler? MessageReceived;
+
+    /// <summary>
+    /// Event raised when the channel connection state changes
+    /// </summary>
+    event ChannelConnectionChangedEventHandler? ConnectionStateChanged;
+
+    /// <summary>
+    /// Send a message to the channel
+    /// </summary>
+    /// <param name="message">The message to send</param>
+    /// <param name="cancellationToken">Cancellation token</param>
+    /// <returns>Task representing the send operation</returns>
+    Task SendMessageAsync(ChannelMessage message, CancellationToken cancellationToken = default);
+
+    /// <summary>
+    /// Send a streaming response to the channel
+    /// </summary>
+    /// <param name="messageStream">Async enumerable of response updates</param>
+    /// <param name="cancellationToken">Cancellation token</param>
+    /// <returns>Task representing the send operation</returns>
+    Task SendStreamingMessageAsync(IAsyncEnumerable<ChatStreamUpdate> messageStream, CancellationToken cancellationToken = default);
+}

Luna.Channels.Abstractions/IChannelManager.cs

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+namespace Luna.Channels.Abstractions;
+
+/// <summary>
+/// Manages the lifecycle and routing of all registered communication channels.
+/// </summary>
+public interface IChannelManager
+{
+    /// <summary>
+    /// Registers a channel with this manager.
+    /// </summary>
+    /// <param name="channel"></param>
+    /// <exception cref="InvalidOperationException">Thrown if a channel with the same ID is already registered.</exception>
+    void RegisterChannel(IChannel channel);
+
+    /// <summary>
+    /// Unregisters a channel by its ID. No-op if the channel is not found.
+    /// </summary>
+    /// <param name="channelId">The ID of the channel to remove.</param>
+    void UnregisterChannel(string channelId);
+
+    /// <summary>
+    /// Retrieves a registered channel by its ID.
+    /// </summary>
+    /// <param name="channelId">The ID of the channel to retrieve.</param>
+    /// <returns>The channel, or null if not found.</returns>
+    IChannel? GetChannel(string channelId);
+
+    /// <summary>
+    /// Returns all currently registered channels.
+    /// </summary>
+    IReadOnlyList<IChannel> GetAllChannels();
+
+    /// <summary>
+    /// Raised after a message has been received and routed.
+    /// </summary>
+    event EventHandler<ChannelMessageReceivedEventArgs>? MessageRouted;
+}

Luna.Channels.Abstractions/Luna.Channels.Abstractions.csproj

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+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <TargetFramework>net10.0</TargetFramework>
+    <ImplicitUsings>enable</ImplicitUsings>
+    <Nullable>enable</Nullable>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <ProjectReference Include="..\Luna.Shared\Luna.Shared.csproj" />
+  </ItemGroup>
+
+</Project>