Offline POS sales and automatic background sync

The POS terminal is architected to ensure uninterrupted retail transactions even when internet connectivity drops. 1. Local Catalog Caching: Active products, barcodes, prices, and tax rates are securely cached in the browser local storage upon shift opening. 2. Offline Order Processing: When offline mode is active, the POS continues to scan items, calculate taxes, accept cash payments, and print local receipts. 3. Transaction Queue: Offline receipts receive temporary unique sequential tokens and are queued locally. 4. Automatic Synchronization: As soon as network connectivity is restored, the terminal automatically streams queued transactions to the server in chronological batches, updates inventory balances, and generates official posted invoice records.