android: use embedded QR scanner for borrow/return

android/build.gradle

@@ -112,6 +112,8 @@ dependencies {
     implementation 'androidx.camera:camera-camera2:1.3.1'
     implementation 'androidx.camera:camera-lifecycle:1.3.1'
     implementation 'androidx.camera:camera-view:1.3.1'
+    implementation 'com.journeyapps:zxing-android-embedded:4.3.0'
+    implementation 'com.google.zxing:core:3.5.0'
     // implementation project(':backend')  // 注释掉backend依赖，因为它包含Spring Boot不适合Android
     
     testImplementation 'junit:junit:4.13.2'

android/src/main/java/com/smartlibrary/android/MainActivity.java

@@ -25,6 +25,7 @@ import androidx.core.content.ContextCompat;
 import androidx.recyclerview.widget.LinearLayoutManager;
 import androidx.recyclerview.widget.RecyclerView;
 
+import com.google.zxing.integration.android.IntentIntegrator;
 import com.smartlibrary.R;
 import com.smartlibrary.android.ai.VoiceService;
 import com.smartlibrary.android.data.DataManager;
@@ -1611,13 +1612,17 @@ public class MainActivity extends AppCompatActivity {
 
     private void startScan(int requestCode) {
         try {
-            Intent intent = new Intent("com.google.zxing.client.android.SCAN");
-            intent.putExtra("SCAN_MODE", "QR_CODE_MODE");
-            startActivityForResult(intent, requestCode);
-        } catch (Exception e) {
+            IntentIntegrator integrator = new IntentIntegrator(this);
+            integrator.setDesiredBarcodeFormats(IntentIntegrator.QR_CODE);
+            integrator.setOrientationLocked(false);
+            integrator.setBeepEnabled(true);
+            integrator.setPrompt("对准图书二维码进行扫描");
+            integrator.setRequestCode(requestCode);
+            integrator.initiateScan();
+        } catch (Throwable t) {
             new AlertDialog.Builder(this)
-                    .setTitle("未找到扫码应用")
-                    .setMessage("请先安装支持二维码扫描的应用（如 ZXing Barcode Scanner），然后重新尝试扫码借阅/还书；或在图书列表中手动操作。")
+                    .setTitle("扫码功能不可用")
+                    .setMessage("初始化内置扫码功能失败，请检查相机权限，或在图书列表中手动操作借阅/还书。")
                     .setPositiveButton("确定", null)
                     .show();
         }