fix: send Telegram deployment notification asynchronously

- Move deployment completion alert to background Task
- Prevent blocking app startup waiting for Telegram API
- Fixes 'service not responding' errors during health check
- Add error handling for Telegram send failures

Co-Authored-By: Claude Haiku 4.5 <noreply@anthropic.com>

TaxBaik.Web/Program.cs

@@ -232,14 +232,24 @@ try
     Log.Information("애플리케이션 시작: {Environment}", app.Environment.EnvironmentName);
     if (!app.Environment.IsDevelopment())
     {
-        using (var scope = app.Services.CreateScope())
+        // 배포 완료 알림을 백그라운드에서 비동기 전송 (앱 시작 블록 방지)
+        _ = Task.Run(async () =>
         {
-            var telegramService = scope.ServiceProvider.GetRequiredService<ITelegramNotificationService>();
-            // 배포 완료 알림
-            await telegramService.SendInfoAsync(
-                "✅ 배포 완료",
-                $"환경: {app.Environment.EnvironmentName}\n상태: 정상 운영 중");
-        }
+            try
+            {
+                using (var scope = app.Services.CreateScope())
+                {
+                    var telegramService = scope.ServiceProvider.GetRequiredService<ITelegramNotificationService>();
+                    await telegramService.SendInfoAsync(
+                        "✅ 배포 완료",
+                        $"환경: {app.Environment.EnvironmentName}\n상태: 정상 운영 중");
+                }
+            }
+            catch (Exception ex)
+            {
+                Log.Error(ex, "배포 완료 알림 전송 실패");
+            }
+        });
     }
     app.Run();
 }
@@ -248,12 +258,19 @@ catch (Exception ex)
     Log.Fatal(ex, "애플리케이션 강종");
     if (!app.Environment.IsDevelopment())
     {
-        using (var scope = app.Services.CreateScope())
+        try
         {
-            var telegramService = scope.ServiceProvider.GetRequiredService<ITelegramNotificationService>();
-            await telegramService.SendErrorAsync(
-                "❌ 서버 오류",
-                $"환경: {app.Environment.EnvironmentName}\n오류: {ex.Message}");
+            using (var scope = app.Services.CreateScope())
+            {
+                var telegramService = scope.ServiceProvider.GetRequiredService<ITelegramNotificationService>();
+                await telegramService.SendErrorAsync(
+                    "❌ 서버 오류",
+                    $"환경: {app.Environment.EnvironmentName}\n오류: {ex.Message}");
+            }
+        }
+        catch (Exception telegramEx)
+        {
+            Log.Error(telegramEx, "오류 알림 전송 실패");
         }
     }
     throw;