feat: add CheckAndInstallAsync convenience method to UpdateManager

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

MosswartMassacre/UpdateManager.cs

@@ -206,6 +206,26 @@ namespace MosswartMassacre
             }
         }
         
+        /// <summary>
+        /// Check for update and auto-install if available. Used by startup auto-update.
+        /// </summary>
+        public static async Task CheckAndInstallAsync()
+        {
+            try
+            {
+                bool checkOk = await CheckForUpdateAsync();
+                if (checkOk && updateAvailable)
+                {
+                    PluginCore.WriteToChat("[Update] Auto-installing update...");
+                    await DownloadAndInstallUpdateAsync();
+                }
+            }
+            catch (Exception ex)
+            {
+                PluginCore.WriteToChat($"[Update] Auto-update failed: {ex.Message}");
+            }
+        }
+
         private static string GetLocalDllPath()
         {
             // Get the path to the current DLL