feat: implement background update check and add version notification in AppOrchestrator

src/EchoHub.Client/Services/UpdateChecker.cs

@@ -0,0 +1,47 @@
+using System.Net.Http.Json;
+using System.Text.Json.Serialization;
+
+namespace EchoHub.Client.Services;
+
+public static class UpdateChecker
+{
+    private static readonly Uri ReleaseUrl =
+        new("https://api.github.com/repos/HueByte/EchoHub/releases/latest");
+
+    /// <summary>
+    /// Checks GitHub for a newer release. Returns the new version string if one exists, or null.
+    /// Never throws — all errors are silently swallowed.
+    /// </summary>
+    public static async Task<string?> CheckForUpdateAsync()
+    {
+        try
+        {
+            using var http = new HttpClient { Timeout = TimeSpan.FromSeconds(5) };
+            http.DefaultRequestHeaders.UserAgent.ParseAdd("EchoHub-Client");
+
+            var release = await http.GetFromJsonAsync<GitHubRelease>(ReleaseUrl);
+            if (release?.TagName is null)
+                return null;
+
+            var tag = release.TagName.TrimStart('v', 'V');
+            if (!Version.TryParse(tag, out var latest))
+                return null;
+
+            var currentStr = typeof(UpdateChecker).Assembly.GetName().Version?.ToString(3);
+            if (currentStr is null || !Version.TryParse(currentStr, out var current))
+                return null;
+
+            return latest > current ? tag : null;
+        }
+        catch
+        {
+            return null;
+        }
+    }
+
+    private sealed class GitHubRelease
+    {
+        [JsonPropertyName("tag_name")]
+        public string? TagName { get; set; }
+    }
+}