Build Bulk Voucher System

Hello,
I am looking for an experienced Full-Stack Developer to build a secure, mobile-optimized web application for a charitable charity initiative. The system will manage printed charity vouchers and verify them in bulk via a smartphone camera directly through the web browser (no mobile app download required).
I already have the front-end user interface (HTML & CSS) ready, fully optimized for mobile devices and written in English. Your role will be to build the robust backend, design the database, and programmatically integrate the continuous camera scanning functionality.
Technical Requirements
1. Admin Dashboard
Serial Number Generator: A secure system to generate thousands of unique, random 9-digit serial numbers.
Bulk Export: Ability to export generated serial numbers into Excel/PDF formats to send to the printing press.
Agent Management: A module to manage agent (cashier/money exchanger) accounts, track their balances, and view transaction history.
Manual Settlement: A feature to manually settle and reset an agent's outstanding balance after they are paid.
2. Agent / Money Exchanger Dashboard (Mobile Optimized)
Secure Login: A protected login interface tailor-made for mobile viewports.
Continuous Bulk Scanning: Integration of a web-based scanning library (such as Html5-QRCode or QuaggaJS). The camera must remain open to allow rapid, successive scanning of barcodes or serial numbers.
Real-Time Validation: Live verification against the database for every scanned voucher. Valid vouchers must show a green indicator and increase the session counter. Used or fake vouchers must flash red and trigger an error alert.
Bulk Redeem Button: A "Confirm & Redeem Cash" button that updates all scanned vouchers to "Used" in the database instantly and credits the total value to the agent's account.
3. Security & Integrity
Race Condition Prevention: The system must prevent concurrent exploitation attacks (e.g., trying to scan/redeem the exact same voucher at the same millisecond from two different devices) using robust Database Transactions and Row Locking.
Developer Requirements
Proven experience with relational databases (MySQL, PostgreSQL) or Firebase.
Experience integrating web-based barcode/QR scanning libraries.
Ability to deliver clean, documented, and secure code.
Full system testing must be completed before final hand-off.
The HTML/CSS template files and exact project logic rules are ready to be shared with the selected candidate.
Please submit your proposal detailing:
The tech stack you intend to use (Node.js, PHP/Laravel, Python/Django, etc.).
Your estimated timeline for completion.
Examples of similar dashboards or web-cam tools you have built