Implement and polish invoice/bill scan transaction flow

[gjong]

Summary

• add end-to-end invoice/bill scan MVP flow:
  • dashboard FAB action for scan
  • scan screen + scan view model
  • on-device OCR with ML Kit
  • backend text-to-transaction extraction wiring
  • prefill handoff into existing add-transaction form
• improve scan UX to be easier and more visually appealing:
  • guided 3-step layout (Import -> Extract -> Review)
  • clearer section cards, status/progress feedback, and larger primary actions
  • richer draft preview with icons and confidence badge
  • sticky bottom CTA when draft is ready
  • explicit manual-entry fallback action
  • improved error card styling and helper copy
• fix Kotlin compile issue on scan screen:
  • resolve smart-cast problem by capturing uiState.draft in a stable local value before lambda usage
• localize scan feature text completely:
  • move remaining hardcoded scan error copy into string resources
  • add Dutch (values-nl) and German (values-de) translations for scan/FAB strings
• add camera capture support in scan flow:
  • add Take a photo action next to gallery import
  • use ActivityResultContracts.TakePicture() with temporary content:// URI
  • configure FileProvider + res/xml/file_paths.xml for secure camera output
  • handle camera launch failures with localized error copy
• fix camera button behavior when permission is missing:
  • explicitly request runtime CAMERA permission before capture
  • show localized errors when permission is denied or when no camera app is available
  • only launch camera intent after permission grant and camera-app availability check
• improve OCR for invoice/bill tables with description + price columns:
  • add OcrTextFormatter to reconstruct row-aligned text from OCR bounding boxes
  • detect two-column layouts and pair left description cells with right amount cells by Y-position
  • emit cleaner tab-separated lines for better downstream transaction extraction
  • include unit tests for two-column pairing and single-column fallback behavior

Technical details

• added TransactionExtractionDraft domain model
• extended TransactionRepository with extractTransactionFromText(text)
• wired extraction call in PledgerApiService
• mapped extraction payload in TransactionRepositoryImpl
• added InvoiceTextExtractor (ML Kit text recognition)
• added InvoiceScanScreen + InvoiceScanViewModel
• extended add-transaction route to accept optional prefill query params, parsed by TransactionFormViewModel

Testing

• Added unit tests: OcrTextFormatterTest
• Attempted compile/tests in cloud environment but Android SDK is not configured (ANDROID_HOME / local.properties missing)