feat: add GitHub release API client and response DTOs

Services/GithubService.cs

@@ -1,6 +1,57 @@
+using System.Text.Json;
+using System.Text.Json.Serialization;
+using ForgejoReleaseSync.DTOs;
+using Microsoft.Extensions.Logging;
+
 namespace ForgejoReleaseSync.Services;
 
 public class GithubService
 {
     
+    private readonly AppConfig _config;
+    private readonly RepositoryConfig _repoConfig;
+    private readonly HttpClient _httpClient;
+    private readonly ILogger<GithubService> _logger;
+    
+    public GithubService(AppConfig config, RepositoryConfig repoConfig, ILogger<GithubService> logger)
+    {
+        var client = new HttpClient();
+        client.BaseAddress = new Uri("https://api.github.com");
+        client.DefaultRequestHeaders.Add("User-Agent", "ForgejoReleaseSync");
+        client.DefaultRequestHeaders.Add("Accept", "application/json");
+        client.Timeout = TimeSpan.FromSeconds(90);
+
+        _config = config;
+        _repoConfig = repoConfig;
+        _httpClient = client;
+        _logger = logger;
+    }
+    
+    
+    public async Task<List<GithubReleaseResponseDto>> FetchRepoReleasesAsync(string owner, string repo)
+    {
+        try
+        {
+            var response = await _httpClient.GetAsync(
+                $"/repos/{owner}/{repo}/releases?per_page=3&page=1");
+
+            response.EnsureSuccessStatusCode();
+
+            var responseStream = await response.Content.ReadAsStreamAsync();
+            var releases = await JsonSerializer.DeserializeAsync(responseStream,
+                AppJsonSerializerContext.Default.ListGithubReleaseResponseDto);
+
+            return releases ?? [];
+        }
+        catch (Exception ex)
+        {
+            _logger.LogError(ex, "Failed to fetch posts from Mastodon");
+            return [];
+        }
+    }
+}
+
+[JsonSerializable(typeof(List<GithubReleaseResponseDto>))]
+internal partial class AppJsonSerializerContext : JsonSerializerContext
+{
 }