feat: Implement OpenRouter API client for managing headers and retrieving model pricing.

OpenRouter/OpenRouterHeaders.cs

@@ -0,0 +1,19 @@
+using System.Net.Http;
+
+namespace AnchorCli.OpenRouter;
+
+/// <summary>
+/// Provides extension methods for adding OpenRouter-specific HTTP headers.
+/// </summary>
+public static class OpenRouterHeaders
+{
+    /// <summary>
+    /// Applies the required OpenRouter headers to the specified HttpClient.
+    /// </summary>
+    public static void ApplyTo(HttpClient httpClient)
+    {
+        httpClient.DefaultRequestHeaders.TryAddWithoutValidation("HTTP-Referer", "https://git.technopunk.space/tomi/AnchorCli");
+        httpClient.DefaultRequestHeaders.TryAddWithoutValidation("X-OpenRouter-Title", "Anchor CLI");
+        httpClient.DefaultRequestHeaders.TryAddWithoutValidation("X-OpenRouter-Categories", "cli-agent");
+    }
+}

OpenRouter/PricingProvider.cs

@@ -14,6 +14,11 @@ internal sealed class PricingProvider
     private static readonly HttpClient Http = new();
     private Dictionary<string, ModelInfo>? _models;
 
+    static PricingProvider()
+    {
+        OpenRouterHeaders.ApplyTo(Http);
+    }
+
     /// <summary>
     /// Fetches the full model list from OpenRouter (cached after first call).
     /// </summary>