fix(ios): align deployment target to 15.0 and link mlkit barcode pod

- All four IPHONEOS_DEPLOYMENT_TARGET entries in project.pbxproj bumped
  from 13.0 to 15.0 to match Podfile's 'platform :ios, 15.0' and
  Capacitor 8's minimum. Mismatched target caused Swift compile errors
  for iOS-15-only APIs in linked pods.
- Add CapacitorMlkitBarcodeScanning pod to Podfile and the package to
  root package.json (already in frontend/package.json). Without this,
  cap sync never linked the pod and the build failed with
  'No such module CapacitorMLKitBarcodeScanning'.

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

ios/App/Podfile

@@ -12,6 +12,7 @@ def capacitor_pods
   pod 'Capacitor', :path => '../../node_modules/@capacitor/ios'
   pod 'CapacitorCordova', :path => '../../node_modules/@capacitor/ios'
   pod 'CapacitorApp', :path => '../../node_modules/@capacitor/app'
+  pod 'CapacitorMlkitBarcodeScanning', :path => '../../node_modules/@capacitor-mlkit/barcode-scanning'
   pod 'CapacitorSplashScreen', :path => '../../node_modules/@capacitor/splash-screen'
   pod 'CapacitorStatusBar', :path => '../../node_modules/@capacitor/status-bar'
 end