refactor: reduce notification spam and focus on deployment alerts

- Remove login success notifications (only log to file)
- Remove login failure notifications (only log to file)
- Add deployment completion notification
- Add error notifications for server crashes
- Notifications now only on critical events (deploy/error)

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

TaxBaik.Web/Program.cs

@@ -235,9 +235,10 @@ try
         using (var scope = app.Services.CreateScope())
         {
             var telegramService = scope.ServiceProvider.GetRequiredService<ITelegramNotificationService>();
+            // 배포 완료 알림
             await telegramService.SendInfoAsync(
-                "서버 시작",
-                $"환경: {app.Environment.EnvironmentName}");
+                "✅ 배포 완료",
+                $"환경: {app.Environment.EnvironmentName}\n상태: 정상 운영 중");
         }
     }
     app.Run();
@@ -251,7 +252,7 @@ catch (Exception ex)
         {
             var telegramService = scope.ServiceProvider.GetRequiredService<ITelegramNotificationService>();
             await telegramService.SendErrorAsync(
-                "서버 오류",
+                "❌ 서버 오류",
                 $"환경: {app.Environment.EnvironmentName}\n오류: {ex.Message}");
         }
     }