Add Luna.Configuration with TOML-based agent and provider config

Implement configuration system with embedded TOML resources for agent
and provider definitions, custom IConfigurationSource/Provider for
agent and provider options, and DI extension methods. Includes config
models for agents, providers, sessions, and Telegram integration.

Luna.Configuration/Services/Agents/AgentOptionsConfigurationSource.cs

@@ -0,0 +1,12 @@
+using Microsoft.Extensions.Configuration;
+
+namespace Luna.Configuration.Services.Agents;
+
+internal class AgentOptionsConfigurationSource(string? searchPath = null)
+    : IConfigurationSource
+{
+    private readonly AgentOptionsProvider optionsProvider = new(searchPath);
+
+    public IConfigurationProvider Build(IConfigurationBuilder builder)
+        => new AgentOptionsConfigurationProvider(optionsProvider.GetAgentOptions());
+}