- Add camera, google_mlkit_text_recognition, image_picker, permission_handler deps
- Create ScannerScreen with live camera preview and OCR text recognition
- Auto-detect Hot Wheels IDs (e.g. JKF21) from captured photos using regex
- Add manual entry fallback dialog for typing HW ID by hand
- Update HomeScreen with scan FAB button and full DB query flow
- Query hotwheels table with .eq('hw_id', scannedCode).maybeSingle()
- Show 'Already in Collection' alert if car exists
- Show 'Add to Collection?' confirmation with insert if car is new
