When a barcode is not found in Open Food Facts, the service now tries
Open Beauty Facts and Open Products Facts before giving up. All three
share the same API format; only the host URL differs.
When all databases miss, the scan endpoint sets needs_manual_entry=true
in the result. The frontend detects this, shows a calm informational
message, and switches to manual entry mode automatically.
Also fixes a latent bug where not-found scans showed 'Added: item to
pantry' due to the success condition checking barcodes_found (always 1)
instead of added_to_inventory.
Closes#65
pyr0ball
0de6182f48