Fix: 앱 재시작 시 UI 상태와 서비스 상태 동기화 문제 해결

onResume()에서 실제 FTPService 실행 상태를 확인하여 UI를 동기화함으로써 화면 전환 또는 앱 재시작 시에도 올바른 버튼 상태가 표시되도록 수정.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

app/src/main/java/be/gyu/android/server/ftp/MainActivity.java

@@ -8,6 +8,8 @@ import androidx.core.content.ContextCompat;
 import androidx.documentfile.provider.DocumentFile;
 
 import android.Manifest;
+import android.app.ActivityManager;
+import android.content.Context;
 import android.content.Intent;
 import android.content.pm.PackageManager;
 import android.net.Uri;
@@ -239,4 +241,27 @@ public class MainActivity extends AppCompatActivity {
             }
         }
     }
+
+    /**
+     * Check if FTPService is currently running in the background
+     */
+    private boolean isServiceRunning() {
+        ActivityManager manager = (ActivityManager) getSystemService(Context.ACTIVITY_SERVICE);
+        if (manager != null) {
+            for (ActivityManager.RunningServiceInfo service : manager.getRunningServices(Integer.MAX_VALUE)) {
+                if (FTPService.class.getName().equals(service.service.getClassName())) {
+                    return true;
+                }
+            }
+        }
+        return false;
+    }
+
+    @Override
+    protected void onResume() {
+        super.onResume();
+        // Sync UI with actual service state when activity resumes
+        isServerRunning = isServiceRunning();
+        updateUI();
+    }
 }