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

Providers/OllamaTokenExtractor.cs

@@ -0,0 +1,39 @@
+using System.Net.Http.Headers;
+
+namespace AnchorCli.Providers;
+
+/// <summary>
+/// Token extractor for Ollama responses.
+/// Ollama doesn't provide official token counts, so we estimate.
+/// </summary>
+internal sealed class OllamaTokenExtractor : ITokenExtractor
+{
+    public string ProviderName => "Ollama";
+
+    public (int inputTokens, int outputTokens)? ExtractTokens(HttpResponseHeaders headers, string? responseBody)
+    {
+        // Ollama doesn't provide token headers
+        return null;
+    }
+
+    public int? ExtractLatency(HttpResponseHeaders headers)
+    {
+        // Ollama doesn't provide latency headers
+        return null;
+    }
+
+    /// <summary>
+    /// Estimates token count from text length (rough approximation).
+    /// Assumes ~4 characters per token on average.
+    /// </summary>
+    public static int EstimateTokens(string text)
+    {
+        if (string.IsNullOrEmpty(text))
+        {
+            return 0;
+        }
+
+        // Rough estimate: 4 characters per token
+        return text.Length / 4;
+    }
+}