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

Providers/OpenRouterProvider.cs

@@ -0,0 +1,40 @@
+using System.Net.Http.Json;
+using System.Text.Json;
+using AnchorCli.OpenRouter;
+
+namespace AnchorCli.Providers;
+
+/// <summary>
+/// Pricing provider for OpenRouter API.
+/// </summary>
+internal sealed class OpenRouterProvider : IPricingProvider
+{
+    private const string ModelsUrl = "https://openrouter.ai/api/v1/models";
+    private static readonly HttpClient Http = new();
+    private Dictionary<string, ModelInfo>? _models;
+
+    static OpenRouterProvider()
+    {
+        OpenRouterHeaders.ApplyTo(Http);
+    }
+
+    public async Task<Dictionary<string, ModelInfo>> GetAllModelsAsync(CancellationToken ct = default)
+    {
+        if (_models != null) return _models;
+
+        var response = await Http.GetAsync(ModelsUrl, ct);
+        response.EnsureSuccessStatusCode();
+
+        var json = await response.Content.ReadAsStringAsync(ct);
+        var result = JsonSerializer.Deserialize(json, AppJsonContext.Default.ModelsResponse);
+
+        _models = result?.Data?.ToDictionary(m => m.Id) ?? [];
+        return _models;
+    }
+
+    public async Task<ModelInfo?> GetModelInfoAsync(string modelId, CancellationToken ct = default)
+    {
+        var models = await GetAllModelsAsync(ct);
+        return models.GetValueOrDefault(modelId);
+    }
+}