Add scanned page image export sample

[advanc3dUA]

Summary

Adds an image export flow to the sample app, demonstrating how to save each scanned or imported document page as JPG files.

What changed

• Added an Image Export option to the main sample list.
• Reused the existing scan/PDF/image input flow.
• Exported all document pages with Document.pageCount() and Document.writeImage(page:fileUrl:).
• Presented the exported JPG files with the system share sheet.
• Added English and German localized strings with an English fallback for other locales.

Verification

• Built successfully with xcodebuild:
  xcodebuild -project DocutainSDKExampleiOSSwift.xcodeproj -scheme DocutainSDKExampleiOSSwift -configuration Debug -sdk iphonesimulator -destination 'generic/platform=iOS Simulator' CODE_SIGNING_ALLOWED=NO build
• Runtime testing on a physical device could not be completed because obtaining a Docutain trial license from the website failed during verification.