Visitor QR Check-In App

I’m building a simple yet secure solution that lets visitors enter and leave our gated community by scanning a QR code. The core flow is straightforward:

• Residents create a unique, time-bound QR code for each guest from within the same app (or their own resident view).
• The visitor presents that code at the gate, security scans it, and the visit is automatically logged as “checked-in.”
• On departure the guard scans again, closing the visit record as “checked-out.”

That check-in / check-out cycle is the only must-have for this first version. I do not need broader resident-notification features or an elaborate security dashboard right now—speed and reliability of the QR workflow are my priorities.

Deliverables I expect:
1. Cross-platform mobile app (Android + iOS) with two roles: Resident (code generator) and Security (scanner).
2. Backend that stores visit logs securely and lets me export basic reports (CSV or similar).
3. Simple admin credentials so I can add/remove residents myself.
4. Brief deployment guide and source code.

Acceptance criteria:
• A visitor can’t be checked in unless the QR is valid, unused, and within its active window.
• Duplicate or expired codes are rejected with a clear message.
• All successful scans instantly create or close a record in the database, visible in an activity log.
• App loads and scanning complete in under two seconds on a mid-range device.

I’m flexible on the tech stack; Flutter + Firebase or React Native + Supabase are both fine if they meet the above speed and security targets. Let me know your proposed approach, timeline, and any past work using QR code workflows.