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

@@ -0,0 +1,27 @@
+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; }
+}