refactor(QRScanner): Align with platform service architecture

- Reorganize QR scanner to follow platform service pattern
- Move QR scanner implementations to services/platforms directory
- Update QRScannerFactory to use PlatformServiceFactory pattern
- Consolidate common QR scanner interfaces with platform services
- Add proper error handling and logging across implementations
- Ensure consistent cleanup and lifecycle management
- Add PyWebView implementation placeholder for desktop
- Update Capacitor and Web implementations to match platform patterns

src/services/QRScanner/NativeQRScanner.ts

@@ -0,0 +1,88 @@
+import {
+  BarcodeScanner,
+  BarcodeFormat,
+  LensFacing,
+} from "@capacitor-mlkit/barcode-scanning";
+import type { PluginListenerHandle } from "@capacitor/core";
+import { QRScannerService, ScanListener } from "./types";
+
+export class NativeQRScanner implements QRScannerService {
+  private scanListener: ScanListener | null = null;
+  private isScanning = false;
+  private listenerHandle: PluginListenerHandle | null = null;
+
+  async checkPermissions(): Promise<boolean> {
+    const { camera } = await BarcodeScanner.checkPermissions();
+    return camera === "granted";
+  }
+
+  async requestPermissions(): Promise<boolean> {
+    const { camera } = await BarcodeScanner.requestPermissions();
+    return camera === "granted";
+  }
+
+  async isSupported(): Promise<boolean> {
+    const { supported } = await BarcodeScanner.isSupported();
+    return supported;
+  }
+
+  async startScan(): Promise<void> {
+    if (this.isScanning) {
+      throw new Error("Scanner is already running");
+    }
+
+    try {
+      this.isScanning = true;
+      await BarcodeScanner.startScan({
+        formats: [BarcodeFormat.QrCode],
+        lensFacing: LensFacing.Back,
+      });
+
+      this.listenerHandle = await BarcodeScanner.addListener(
+        "barcodesScanned",
+        async (result) => {
+          if (result.barcodes.length > 0 && this.scanListener) {
+            const barcode = result.barcodes[0];
+            this.scanListener.onScan(barcode.rawValue);
+            await this.stopScan();
+          }
+        },
+      );
+    } catch (error) {
+      this.isScanning = false;
+      if (this.scanListener?.onError) {
+        this.scanListener.onError(new Error(String(error)));
+      }
+      throw error;
+    }
+  }
+
+  async stopScan(): Promise<void> {
+    if (!this.isScanning) {
+      return;
+    }
+
+    try {
+      await BarcodeScanner.stopScan();
+      this.isScanning = false;
+    } catch (error) {
+      if (this.scanListener?.onError) {
+        this.scanListener.onError(new Error(String(error)));
+      }
+      throw error;
+    }
+  }
+
+  addListener(listener: ScanListener): void {
+    this.scanListener = listener;
+  }
+
+  async cleanup(): Promise<void> {
+    await this.stopScan();
+    if (this.listenerHandle) {
+      await this.listenerHandle.remove();
+      this.listenerHandle = null;
+    }
+    this.scanListener = null;
+  }
+}