Three fixes:
1. Barcode scanner: load ZXing locally with CDN fallback so it works
even when CDN is unreachable.
2. Scan result: add 'Register' button to create a new asset from a
scanned machine_id — works for both found and not-found results.
3. OCR serial search: when extracted machine_id isn't found, also try
searching all numeric strings from OCR text as serial numbers; add
'Register as New Asset' button on OCR not-found result.
