feat: barcode scan visual feedback + EAN checksum validation
- Add scan-status-bar overlay inside scanner viewport showing:
- Active scan method (Native API / Quagga / Native + Quagga)
- Scanning state: ready, scanning, partial read, invalid, confirmed
- Validate EAN-8/EAN-13/UPC checksums in Quagga path before confirming
(native BarcodeDetector validates internally; Quagga can return false positives)
- Show 'invalid barcode, retrying' message with invalid code highlighted
- Reset invalid barcode confidence counter on invalid read so scanner retries
- Spawn parallel Quagga scan with 'combined scan active' status message
- Add 6 translation keys (scan.status_*) in all 5 language files
dadaloop82
bc39361246