feat: Introduce a pluggable LLM provider system with token extraction, pricing, and updated setup configuration.

OpenRouter/TokenTracker.cs

@@ -5,6 +5,7 @@ namespace AnchorCli.OpenRouter;
 /// </summary>
 internal sealed class TokenTracker
 {
+    public string Provider { get; set; } = "Unknown";
     public long SessionInputTokens { get; private set; }
     public long SessionOutputTokens { get; private set; }
     public int RequestCount { get; private set; }
@@ -23,7 +24,6 @@ internal sealed class TokenTracker
 
     /// <summary>Fixed USD per API request.</summary>
     public decimal RequestPrice { get; set; }
-
     /// <summary>
     /// Record usage from one response (may span multiple LLM rounds).
     /// </summary>