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/ChannelType.cs

@@ -0,0 +1,8 @@
+namespace Luna.Channels.Abstractions;
+
+public static class ChannelType
+{
+    public const string Cli = "cli";
+    public const string Web = "web";
+    public const string Telegram = "telegram"; 
+}