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>

package.json

@@ -24,6 +24,7 @@
     "npm-run-all": "^4.1.5"
   },
   "dependencies": {
+    "@capacitor-mlkit/barcode-scanning": "^8.1.0",
     "@capacitor/android": "^8.4.1",
     "@capacitor/app": "^8.1.0",
     "@capacitor/core": "^8.4.1",